Lo-Dash v2.4.1

Arrays

Chaining

Collections

Functions

Objects

Utilities

Methods

Properties

“Arrays” Methods

_.compact(array)

#

Creates an array with all falsey values removed. The values false, null, 0, "", undefined, and NaN are all falsey.

Arguments

  1. array (Array): The array to compact.

Returns

(Array): Returns a new array of filtered values.

Example

_.compact([0, 1, false, 2, '', 3]);
// → [1, 2, 3]

_.difference(array, [values])

#

Creates an array excluding all values of the provided arrays using strict equality for comparisons, i.e. ===.

Arguments

  1. array (Array): The array to process.
  2. [values] (…Array): The arrays of values to exclude.

Returns

(Array): Returns a new array of filtered values.

Example

_.difference([1, 2, 3, 4, 5], [5, 2, 10]);
// → [1, 3, 4]

_.findIndex(array, [callback=identity], [thisArg])

#

This method is like _.find except that it returns the index of the first element that passes the callback check, instead of the element itself.

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. array (Array): The array to search.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(number): Returns the index of the found element, else -1.

Example

var characters = [
  { 'name': 'barney',  'age': 36, 'blocked': false },
  { 'name': 'fred',    'age': 40, 'blocked': true },
  { 'name': 'pebbles', 'age': 1,  'blocked': false }
];

_.findIndex(characters, function(chr) {
  return chr.age < 20;
});
// → 2

// using "_.where" callback shorthand
_.findIndex(characters, { 'age': 36 });
// → 0

// using "_.pluck" callback shorthand
_.findIndex(characters, 'blocked');
// → 1

_.findLastIndex(array, [callback=identity], [thisArg])

#

This method is like _.findIndex except that it iterates over elements of a collection from right to left.

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. array (Array): The array to search.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(number): Returns the index of the found element, else -1.

Example

var characters = [
  { 'name': 'barney',  'age': 36, 'blocked': true },
  { 'name': 'fred',    'age': 40, 'blocked': false },
  { 'name': 'pebbles', 'age': 1,  'blocked': true }
];

_.findLastIndex(characters, function(chr) {
  return chr.age > 30;
});
// → 1

// using "_.where" callback shorthand
_.findLastIndex(characters, { 'age': 36 });
// → 0

// using "_.pluck" callback shorthand
_.findLastIndex(characters, 'blocked');
// → 2

_.first(array, [callback], [thisArg])

#

Gets the first element or first n elements of an array. If a callback is provided elements at the beginning of the array are returned as long as the callback returns truthy. The callback is bound to thisArg and invoked with three arguments; (value, index, array).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Aliases

_.head, _.take

Arguments

  1. array (Array): The array to query.
  2. [callback] (Function|Object|number|string): The function called per element or the number of elements to return. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the first element(s) of array.

Example

_.first([1, 2, 3]);
// → 1

_.first([1, 2, 3], 2);
// → [1, 2]

_.first([1, 2, 3], function(num) {
  return num < 3;
});
// → [1, 2]

var characters = [
  { 'name': 'barney',  'blocked': true,  'employer': 'slate' },
  { 'name': 'fred',    'blocked': false, 'employer': 'slate' },
  { 'name': 'pebbles', 'blocked': true,  'employer': 'na' }
];

// using "_.pluck" callback shorthand
_.first(characters, 'blocked');
// → [{ 'name': 'barney', 'blocked': true, 'employer': 'slate' }]

// using "_.where" callback shorthand
_.pluck(_.first(characters, { 'employer': 'slate' }), 'name');
// → ['barney', 'fred']

_.flatten(array, [isShallow=false], [callback=identity], [thisArg])

#

Flattens a nested array (the nesting can be to any depth). If isShallow is truthy, the array will only be flattened a single level. If a callback is provided each element of the array is passed through the callback before flattening. The callback is bound to thisArg and invoked with three arguments; (value, index, array).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. array (Array): The array to flatten.
  2. [isShallow=false] (boolean): A flag to restrict flattening to a single level.
  3. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  4. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a new flattened array.

Example

_.flatten([1, [2], [3, [[4]]]]);
// → [1, 2, 3, 4];

_.flatten([1, [2], [3, [[4]]]], true);
// → [1, 2, 3, [[4]]];

var characters = [
  { 'name': 'barney', 'age': 30, 'pets': ['hoppy'] },
  { 'name': 'fred',   'age': 40, 'pets': ['baby puss', 'dino'] }
];

// using "_.pluck" callback shorthand
_.flatten(characters, 'pets');
// → ['hoppy', 'baby puss', 'dino']

_.indexOf(array, value, [fromIndex=0])

#

Gets the index at which the first occurrence of value is found using strict equality for comparisons, i.e. ===. If the array is already sorted providing true for fromIndex will run a faster binary search.

Arguments

  1. array (Array): The array to search.
  2. value (*): The value to search for.
  3. [fromIndex=0] (boolean|number): The index to search from or true to perform a binary search on a sorted array.

Returns

(number): Returns the index of the matched value or -1.

Example

_.indexOf([1, 2, 3, 1, 2, 3], 2);
// → 1

_.indexOf([1, 2, 3, 1, 2, 3], 2, 3);
// → 4

_.indexOf([1, 1, 2, 2, 3, 3], 2, true);
// → 2

_.initial(array, [callback=1], [thisArg])

#

Gets all but the last element or last n elements of an array. If a callback is provided elements at the end of the array are excluded from the result as long as the callback returns truthy. The callback is bound to thisArg and invoked with three arguments; (value, index, array).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. array (Array): The array to query.
  2. [callback=1] (Function|Object|number|string): The function called per element or the number of elements to exclude. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a slice of array.

Example

_.initial([1, 2, 3]);
// → [1, 2]

_.initial([1, 2, 3], 2);
// → [1]

_.initial([1, 2, 3], function(num) {
  return num > 1;
});
// → [1]

var characters = [
  { 'name': 'barney',  'blocked': false, 'employer': 'slate' },
  { 'name': 'fred',    'blocked': true,  'employer': 'slate' },
  { 'name': 'pebbles', 'blocked': true,  'employer': 'na' }
];

// using "_.pluck" callback shorthand
_.initial(characters, 'blocked');
// → [{ 'name': 'barney',  'blocked': false, 'employer': 'slate' }]

// using "_.where" callback shorthand
_.pluck(_.initial(characters, { 'employer': 'na' }), 'name');
// → ['barney', 'fred']

_.intersection([array])

#

Creates an array of unique values present in all provided arrays using strict equality for comparisons, i.e. ===.

Arguments

  1. [array] (…Array): The arrays to inspect.

Returns

(Array): Returns an array of shared values.

Example

_.intersection([1, 2, 3], [5, 2, 1, 4], [2, 1]);
// → [1, 2]

_.last(array, [callback], [thisArg])

#

Gets the last element or last n elements of an array. If a callback is provided elements at the end of the array are returned as long as the callback returns truthy. The callback is bound to thisArg and invoked with three arguments; (value, index, array).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. array (Array): The array to query.
  2. [callback] (Function|Object|number|string): The function called per element or the number of elements to return. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the last element(s) of array.

Example

_.last([1, 2, 3]);
// → 3

_.last([1, 2, 3], 2);
// → [2, 3]

_.last([1, 2, 3], function(num) {
  return num > 1;
});
// → [2, 3]

var characters = [
  { 'name': 'barney',  'blocked': false, 'employer': 'slate' },
  { 'name': 'fred',    'blocked': true,  'employer': 'slate' },
  { 'name': 'pebbles', 'blocked': true,  'employer': 'na' }
];

// using "_.pluck" callback shorthand
_.pluck(_.last(characters, 'blocked'), 'name');
// → ['fred', 'pebbles']

// using "_.where" callback shorthand
_.last(characters, { 'employer': 'na' });
// → [{ 'name': 'pebbles', 'blocked': true, 'employer': 'na' }]

_.lastIndexOf(array, value)

#

Gets the index at which the last occurrence of value is found using strict equality for comparisons, i.e. ===. If fromIndex is negative, it is used as the offset from the end of the collection.

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. array (Array): The array to search.
  2. value (*): The value to search for.
  3. [fromIndex=array.length-1] (number): The index to search from.

Returns

(number): Returns the index of the matched value or -1.

Example

_.lastIndexOf([1, 2, 3, 1, 2, 3], 2);
// → 4

_.lastIndexOf([1, 2, 3, 1, 2, 3], 2, 3);
// → 1

_.pull(array, [value])

#

Removes all provided values from the given array using strict equality for comparisons, i.e. ===.

Arguments

  1. array (Array): The array to modify.
  2. [value] (…*): The values to remove.

Returns

(Array): Returns array.

Example

var array = [1, 2, 3, 1, 2, 3];
_.pull(array, 2, 3);
console.log(array);
// → [1, 1]

_.range([start=0], end, [step=1])

#

Creates an array of numbers (positive and/or negative) progressing from start up to but not including end. If start is less than stop a zero-length range is created unless a negative step is specified.

Arguments

  1. [start=0] (number): The start of the range.
  2. end (number): The end of the range.
  3. [step=1] (number): The value to increment or decrement by.

Returns

(Array): Returns a new range array.

Example

_.range(4);
// → [0, 1, 2, 3]

_.range(1, 5);
// → [1, 2, 3, 4]

_.range(0, 20, 5);
// → [0, 5, 10, 15]

_.range(0, -4, -1);
// → [0, -1, -2, -3]

_.range(1, 4, 0);
// → [1, 1, 1]

_.range(0);
// → []

_.remove(array, [callback=identity], [thisArg])

#

Removes all elements from an array that the callback returns truthy for and returns an array of removed elements. The callback is bound to thisArg and invoked with three arguments; (value, index, array).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. array (Array): The array to modify.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a new array of removed elements.

Example

var array = [1, 2, 3, 4, 5, 6];
var evens = _.remove(array, function(num) { return num % 2 == 0; });

console.log(array);
// → [1, 3, 5]

console.log(evens);
// → [2, 4, 6]

_.rest(array, [callback=1], [thisArg])

#

The opposite of _.initial this method gets all but the first element or first n elements of an array. If a callback function is provided elements at the beginning of the array are excluded from the result as long as the callback returns truthy. The callback is bound to thisArg and invoked with three arguments; (value, index, array).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Aliases

_.drop, _.tail

Arguments

  1. array (Array): The array to query.
  2. [callback=1] (Function|Object|number|string): The function called per element or the number of elements to exclude. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a slice of array.

Example

_.rest([1, 2, 3]);
// → [2, 3]

_.rest([1, 2, 3], 2);
// → [3]

_.rest([1, 2, 3], function(num) {
  return num < 3;
});
// → [3]

var characters = [
  { 'name': 'barney',  'blocked': true,  'employer': 'slate' },
  { 'name': 'fred',    'blocked': false,  'employer': 'slate' },
  { 'name': 'pebbles', 'blocked': true, 'employer': 'na' }
];

// using "_.pluck" callback shorthand
_.pluck(_.rest(characters, 'blocked'), 'name');
// → ['fred', 'pebbles']

// using "_.where" callback shorthand
_.rest(characters, { 'employer': 'slate' });
// → [{ 'name': 'pebbles', 'blocked': true, 'employer': 'na' }]

_.sortedIndex(array, value, [callback=identity], [thisArg])

#

Uses a binary search to determine the smallest index at which a value should be inserted into a given sorted array in order to maintain the sort order of the array. If a callback is provided it will be executed for value and each element of array to compute their sort ranking. The callback is bound to thisArg and invoked with one argument; (value).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. array (Array): The array to inspect.
  2. value (*): The value to evaluate.
  3. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  4. [thisArg] (*): The this binding of callback.

Returns

(number): Returns the index at which value should be inserted into array.

Example

_.sortedIndex([20, 30, 50], 40);
// → 2

// using "_.pluck" callback shorthand
_.sortedIndex([{ 'x': 20 }, { 'x': 30 }, { 'x': 50 }], { 'x': 40 }, 'x');
// → 2

var dict = {
  'wordToNumber': { 'twenty': 20, 'thirty': 30, 'forty': 40, 'fifty': 50 }
};

_.sortedIndex(['twenty', 'thirty', 'fifty'], 'forty', function(word) {
  return dict.wordToNumber[word];
});
// → 2

_.sortedIndex(['twenty', 'thirty', 'fifty'], 'forty', function(word) {
  return this.wordToNumber[word];
}, dict);
// → 2

_.union([array])

#

Creates an array of unique values, in order, of the provided arrays using strict equality for comparisons, i.e. ===.

Arguments

  1. [array] (…Array): The arrays to inspect.

Returns

(Array): Returns an array of combined values.

Example

_.union([1, 2, 3], [5, 2, 1, 4], [2, 1]);
// → [1, 2, 3, 5, 4]

_.uniq(array, [isSorted=false], [callback=identity], [thisArg])

#

Creates a duplicate-value-free version of an array using strict equality for comparisons, i.e. ===. If the array is sorted, providing true for isSorted will use a faster algorithm. If a callback is provided each element of array is passed through the callback before uniqueness is computed. The callback is bound to thisArg and invoked with three arguments; (value, index, array).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Aliases

_.unique

Arguments

  1. array (Array): The array to process.
  2. [isSorted=false] (boolean): A flag to indicate that array is sorted.
  3. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  4. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a duplicate-value-free array.

Example

_.uniq([1, 2, 1, 3, 1]);
// → [1, 2, 3]

_.uniq([1, 1, 2, 2, 3], true);
// → [1, 2, 3]

_.uniq(['A', 'b', 'C', 'a', 'B', 'c'], function(letter) { return letter.toLowerCase(); });
// → ['A', 'b', 'C']

_.uniq([1, 2.5, 3, 1.5, 2, 3.5], function(num) { return this.floor(num); }, Math);
// → [1, 2.5, 3]

// using "_.pluck" callback shorthand
_.uniq([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x');
// → [{ 'x': 1 }, { 'x': 2 }]

_.without(array, [value])

#

Creates an array excluding all provided values using strict equality for comparisons, i.e. ===.

Arguments

  1. array (Array): The array to filter.
  2. [value] (…*): The values to exclude.

Returns

(Array): Returns a new array of filtered values.

Example

_.without([1, 2, 1, 0, 3, 1, 4], 0, 1);
// → [2, 3, 4]

_.xor([array])

#

Creates an array that is the symmetric difference of the provided arrays. See http://en.wikipedia.org/wiki/Symmetric_difference.

Arguments

  1. [array] (…Array): The arrays to inspect.

Returns

(Array): Returns an array of values.

Example

_.xor([1, 2, 3], [5, 2, 1, 4]);
// → [3, 5, 4]

_.xor([1, 2, 5], [2, 3, 5], [3, 4, 5]);
// → [1, 4, 5]

_.zip([array])

#

Creates an array of grouped elements, the first of which contains the first elements of the given arrays, the second of which contains the second elements of the given arrays, and so on.

Aliases

_.unzip

Arguments

  1. [array] (…Array): Arrays to process.

Returns

(Array): Returns a new array of grouped elements.

Example

_.zip(['fred', 'barney'], [30, 40], [true, false]);
// → [['fred', 30, true], ['barney', 40, false]]

_.zipObject(keys, [values=[]])

#

Creates an object composed from arrays of keys and values. Provide either a single two dimensional array, i.e. [[key1, value1], [key2, value2]] or two arrays, one of keys and one of corresponding values.

Aliases

_.object

Arguments

  1. keys (Array): The array of keys.
  2. [values=[]] (Array): The array of values.

Returns

(Object): Returns an object composed of the given keys and corresponding values.

Example

_.zipObject(['fred', 'barney'], [30, 40]);
// → { 'fred': 30, 'barney': 40 }

“Chaining” Methods

_(value)

#

Creates a lodash object which wraps the given value to enable intuitive method chaining.

In addition to Lo-Dash methods, wrappers also have the following Array methods:
concat, join, pop, push, reverse, shift, slice, sort, splice, and unshift

Chaining is supported in custom builds as long as the value method is implicitly or explicitly included in the build.

The chainable wrapper functions are:
after, assign, bind, bindAll, bindKey, chain, compact, compose, concat, countBy, create, createCallback, curry, debounce, defaults, defer, delay, difference, filter, flatten, forEach, forEachRight, forIn, forInRight, forOwn, forOwnRight, functions, groupBy, indexBy, initial, intersection, invert, invoke, keys, map, max, memoize, merge, min, object, omit, once, pairs, partial, partialRight, pick, pluck, pull, push, range, reject, remove, rest, reverse, shuffle, slice, sort, sortBy, splice, tap, throttle, times, toArray, transform, union, uniq, unshift, unzip, values, where, without, wrap, and zip

The non-chainable wrapper functions are:
clone, cloneDeep, contains, escape, every, find, findIndex, findKey, findLast, findLastIndex, findLastKey, has, identity, indexOf, isArguments, isArray, isBoolean, isDate, isElement, isEmpty, isEqual, isFinite, isFunction, isNaN, isNull, isNumber, isObject, isPlainObject, isRegExp, isString, isUndefined, join, lastIndexOf, mixin, noConflict, parseInt, pop, random, reduce, reduceRight, result, shift, size, some, sortedIndex, runInContext, template, unescape, uniqueId, and value

The wrapper functions first and last return wrapped values when n is provided, otherwise they return unwrapped values.

Explicit chaining can be enabled by using the _.chain method.

Arguments

  1. value (*): The value to wrap in a lodash instance.

Returns

(Object): Returns a lodash instance.

Example

var wrapped = _([1, 2, 3]);

// returns an unwrapped value
wrapped.reduce(function(sum, num) {
  return sum + num;
});
// → 6

// returns a wrapped value
var squares = wrapped.map(function(num) {
  return num * num;
});

_.isArray(squares);
// → false

_.isArray(squares.value());
// → true

_.chain(value)

#

Creates a lodash object that wraps the given value with explicit method chaining enabled.

Arguments

  1. value (*): The value to wrap.

Returns

(Object): Returns the wrapper object.

Example

var characters = [
  { 'name': 'barney',  'age': 36 },
  { 'name': 'fred',    'age': 40 },
  { 'name': 'pebbles', 'age': 1 }
];

var youngest = _.chain(characters)
    .sortBy('age')
    .map(function(chr) { return chr.name + ' is ' + chr.age; })
    .first()
    .value();
// → 'pebbles is 1'

_.tap(value, interceptor)

#

Invokes interceptor with the value as the first argument and then returns value. The purpose of this method is to "tap into" a method chain in order to perform operations on intermediate results within the chain.

Arguments

  1. value (*): The value to provide to interceptor.
  2. interceptor (Function): The function to invoke.

Returns

(*): Returns value.

Example

_([1, 2, 3, 4])
 .tap(function(array) { array.pop(); })
 .reverse()
 .value();
// → [3, 2, 1]

_.prototype.chain()

#

Enables explicit method chaining on the wrapper object.

Returns

(*): Returns the wrapper object.

Example

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

// without explicit chaining
_(characters).first();
// → { 'name': 'barney', 'age': 36 }

// with explicit chaining
_(characters).chain()
  .first()
  .pick('age')
  .value();
// → { 'age': 36 }

_.prototype.toString()

#

Produces the toString result of the wrapped value.

Returns

(string): Returns the string result.

Example

_([1, 2, 3]).toString();
// → '1,2,3'

_.prototype.valueOf()

#

Extracts the wrapped value.

Aliases

_.prototype.value

Returns

(*): Returns the wrapped value.

Example

_([1, 2, 3]).valueOf();
// → [1, 2, 3]

“Collections” Methods

_.at(collection, [index])

#

Creates an array of elements from the specified indexes, or keys, of the collection. Indexes may be specified as individual arguments or as arrays of indexes.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [index] (…(number|number[]|string|string[]): The indexes of collection to retrieve, specified as individual indexes or arrays of indexes.

Returns

(Array): Returns a new array of elements corresponding to the provided indexes.

Example

_.at(['a', 'b', 'c', 'd', 'e'], [0, 2, 4]);
// → ['a', 'c', 'e']

_.at(['fred', 'barney', 'pebbles'], 0, 2);
// → ['fred', 'pebbles']

_.contains(collection, target, [fromIndex=0])

#

Checks if a given value is present in a collection using strict equality for comparisons, i.e. ===. If fromIndex is negative, it is used as the offset from the end of the collection.

Aliases

_.include

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. target (*): The value to check for.
  3. [fromIndex=0] (number): The index to search from.

Returns

(boolean): Returns true if the target element is found, else false.

Example

_.contains([1, 2, 3], 1);
// → true

_.contains([1, 2, 3], 1, 2);
// → false

_.contains({ 'name': 'fred', 'age': 40 }, 'fred');
// → true

_.contains('pebbles', 'eb');
// → true

_.countBy(collection, [callback=identity], [thisArg])

#

Creates an object composed of keys generated from the results of running each element of collection through the callback. The corresponding value of each key is the number of times the key was returned by the callback. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns the composed aggregate object.

Example

_.countBy([4.3, 6.1, 6.4], function(num) { return Math.floor(num); });
// → { '4': 1, '6': 2 }

_.countBy([4.3, 6.1, 6.4], function(num) { return this.floor(num); }, Math);
// → { '4': 1, '6': 2 }

_.countBy(['one', 'two', 'three'], 'length');
// → { '3': 2, '5': 1 }

_.every(collection, [callback=identity], [thisArg])

#

Checks if the given callback returns truthy value for **all** elements of a collection. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Aliases

_.all

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(boolean): Returns true if all elements passed the callback check, else false.

Example

_.every([true, 1, null, 'yes']);
// → false

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

// using "_.pluck" callback shorthand
_.every(characters, 'age');
// → true

// using "_.where" callback shorthand
_.every(characters, { 'age': 36 });
// → false

_.filter(collection, [callback=identity], [thisArg])

#

Iterates over elements of a collection, returning an array of all elements the callback returns truthy for. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Aliases

_.select

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a new array of elements that passed the callback check.

Example

var evens = _.filter([1, 2, 3, 4, 5, 6], function(num) { return num % 2 == 0; });
// → [2, 4, 6]

var characters = [
  { 'name': 'barney', 'age': 36, 'blocked': false },
  { 'name': 'fred',   'age': 40, 'blocked': true }
];

// using "_.pluck" callback shorthand
_.filter(characters, 'blocked');
// → [{ 'name': 'fred', 'age': 40, 'blocked': true }]

// using "_.where" callback shorthand
_.filter(characters, { 'age': 36 });
// → [{ 'name': 'barney', 'age': 36, 'blocked': false }]

_.find(collection, [callback=identity], [thisArg])

#

Iterates over elements of a collection, returning the first element that the callback returns truthy for. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Aliases

_.detect, _.findWhere

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the found element, else undefined.

Example

var characters = [
  { 'name': 'barney',  'age': 36, 'blocked': false },
  { 'name': 'fred',    'age': 40, 'blocked': true },
  { 'name': 'pebbles', 'age': 1,  'blocked': false }
];

_.find(characters, function(chr) {
  return chr.age < 40;
});
// → { 'name': 'barney', 'age': 36, 'blocked': false }

// using "_.where" callback shorthand
_.find(characters, { 'age': 1 });
// →  { 'name': 'pebbles', 'age': 1, 'blocked': false }

// using "_.pluck" callback shorthand
_.find(characters, 'blocked');
// → { 'name': 'fred', 'age': 40, 'blocked': true }

_.findLast(collection, [callback=identity], [thisArg])

#

This method is like _.find except that it iterates over elements of a collection from right to left.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the found element, else undefined.

Example

_.findLast([1, 2, 3, 4], function(num) {
  return num % 2 == 1;
});
// → 3

_.forEach(collection, [callback=identity], [thisArg])

#

Iterates over elements of a collection, executing the callback for each element. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection). Callbacks may exit iteration early by explicitly returning false.

Note: As with other "Collections" methods, objects with a length property are iterated like arrays. To avoid this behavior _.forIn or _.forOwn may be used for object iteration.

Aliases

_.each

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array, Object, string): Returns collection.

Example

_([1, 2, 3]).forEach(function(num) { console.log(num); }).join(',');
// → logs each number and returns '1,2,3'

_.forEach({ 'one': 1, 'two': 2, 'three': 3 }, function(num) { console.log(num); });
// → logs each number and returns the object (property order is not guaranteed across environments)

_.forEachRight(collection, [callback=identity], [thisArg])

#

This method is like _.forEach except that it iterates over elements of a collection from right to left.

Aliases

_.eachRight

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array, Object, string): Returns collection.

Example

_([1, 2, 3]).forEachRight(function(num) { console.log(num); }).join(',');
// → logs each number from right to left and returns '3,2,1'

_.groupBy(collection, [callback=identity], [thisArg])

#

Creates an object composed of keys generated from the results of running each element of a collection through the callback. The corresponding value of each key is an array of the elements responsible for generating the key. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns the composed aggregate object.

Example

_.groupBy([4.2, 6.1, 6.4], function(num) { return Math.floor(num); });
// → { '4': [4.2], '6': [6.1, 6.4] }

_.groupBy([4.2, 6.1, 6.4], function(num) { return this.floor(num); }, Math);
// → { '4': [4.2], '6': [6.1, 6.4] }

// using "_.pluck" callback shorthand
_.groupBy(['one', 'two', 'three'], 'length');
// → { '3': ['one', 'two'], '5': ['three'] }

_.indexBy(collection, [callback=identity], [thisArg])

#

Creates an object composed of keys generated from the results of running each element of the collection through the given callback. The corresponding value of each key is the last element responsible for generating the key. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns the composed aggregate object.

Example

var keys = [
  { 'dir': 'left', 'code': 97 },
  { 'dir': 'right', 'code': 100 }
];

_.indexBy(keys, 'dir');
// → { 'left': { 'dir': 'left', 'code': 97 }, 'right': { 'dir': 'right', 'code': 100 } }

_.indexBy(keys, function(key) { return String.fromCharCode(key.code); });
// → { 'a': { 'dir': 'left', 'code': 97 }, 'd': { 'dir': 'right', 'code': 100 } }

_.indexBy(keys, function(key) { return this.fromCharCode(key.code); }, String);
// → { 'a': { 'dir': 'left', 'code': 97 }, 'd': { 'dir': 'right', 'code': 100 } }

_.invoke(collection, methodName, [arg])

#

Invokes the method named by methodName on each element in the collection returning an array of the results of each invoked method. Additional arguments will be provided to each invoked method. If methodName is a function it will be invoked for, and this bound to, each element in the collection.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. methodName (Function|string): The name of the method to invoke or the function invoked per iteration.
  3. [arg] (…*): Arguments to invoke the method with.

Returns

(Array): Returns a new array of the results of each invoked method.

Example

_.invoke([[5, 1, 7], [3, 2, 1]], 'sort');
// → [[1, 5, 7], [1, 2, 3]]

_.invoke([123, 456], String.prototype.split, '');
// → [['1', '2', '3'], ['4', '5', '6']]

_.map(collection, [callback=identity], [thisArg])

#

Creates an array of values by running each element in the collection through the callback. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Aliases

_.collect

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a new array of the results of each callback execution.

Example

_.map([1, 2, 3], function(num) { return num * 3; });
// → [3, 6, 9]

_.map({ 'one': 1, 'two': 2, 'three': 3 }, function(num) { return num * 3; });
// → [3, 6, 9] (property order is not guaranteed across environments)

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

// using "_.pluck" callback shorthand
_.map(characters, 'name');
// → ['barney', 'fred']

_.max(collection, [callback=identity], [thisArg])

#

Retrieves the maximum value of a collection. If the collection is empty or falsey -Infinity is returned. If a callback is provided it will be executed for each value in the collection to generate the criterion by which the value is ranked. The callback is bound to thisArg and invoked with three arguments; (value, index, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the maximum value.

Example

_.max([4, 2, 8, 6]);
// → 8

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

_.max(characters, function(chr) { return chr.age; });
// → { 'name': 'fred', 'age': 40 };

// using "_.pluck" callback shorthand
_.max(characters, 'age');
// → { 'name': 'fred', 'age': 40 };

_.min(collection, [callback=identity], [thisArg])

#

Retrieves the minimum value of a collection. If the collection is empty or falsey Infinity is returned. If a callback is provided it will be executed for each value in the collection to generate the criterion by which the value is ranked. The callback is bound to thisArg and invoked with three arguments; (value, index, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the minimum value.

Example

_.min([4, 2, 8, 6]);
// → 2

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

_.min(characters, function(chr) { return chr.age; });
// → { 'name': 'barney', 'age': 36 };

// using "_.pluck" callback shorthand
_.min(characters, 'age');
// → { 'name': 'barney', 'age': 36 };

_.pluck(collection, property)

#

Retrieves the value of a specified property from all elements in the collection.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. property (string): The name of the property to pluck.

Returns

(Array): Returns a new array of property values.

Example

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

_.pluck(characters, 'name');
// → ['barney', 'fred']

_.reduce(collection, [callback=identity], [accumulator], [thisArg])

#

Reduces a collection to a value which is the accumulated result of running each element in the collection through the callback, where each successive callback execution consumes the return value of the previous execution. If accumulator is not provided the first element of the collection will be used as the initial accumulator value. The callback is bound to thisArg and invoked with four arguments; (accumulator, value, index|key, collection).

Aliases

_.foldl, _.inject

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [accumulator] (*): Initial value of the accumulator.
  4. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the accumulated value.

Example

var sum = _.reduce([1, 2, 3], function(sum, num) {
  return sum + num;
});
// → 6

var mapped = _.reduce({ 'a': 1, 'b': 2, 'c': 3 }, function(result, num, key) {
  result[key] = num * 3;
  return result;
}, {});
// → { 'a': 3, 'b': 6, 'c': 9 }

_.reduceRight(collection, [callback=identity], [accumulator], [thisArg])

#

This method is like _.reduce except that it iterates over elements of a collection from right to left.

Aliases

_.foldr

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [accumulator] (*): Initial value of the accumulator.
  4. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the accumulated value.

Example

var list = [[0, 1], [2, 3], [4, 5]];
var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []);
// → [4, 5, 2, 3, 0, 1]

_.reject(collection, [callback=identity], [thisArg])

#

The opposite of _.filter this method returns the elements of a collection that the callback does **not** return truthy for.

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a new array of elements that failed the callback check.

Example

var odds = _.reject([1, 2, 3, 4, 5, 6], function(num) { return num % 2 == 0; });
// → [1, 3, 5]

var characters = [
  { 'name': 'barney', 'age': 36, 'blocked': false },
  { 'name': 'fred',   'age': 40, 'blocked': true }
];

// using "_.pluck" callback shorthand
_.reject(characters, 'blocked');
// → [{ 'name': 'barney', 'age': 36, 'blocked': false }]

// using "_.where" callback shorthand
_.reject(characters, { 'age': 36 });
// → [{ 'name': 'fred', 'age': 40, 'blocked': true }]

_.sample(collection, [n])

#

Retrieves a random element or n random elements from a collection.

Arguments

  1. collection (Array|Object|string): The collection to sample.
  2. [n] (number): The number of elements to sample.

Returns

(Array): Returns the random sample(s) of collection.

Example

_.sample([1, 2, 3, 4]);
// → 2

_.sample([1, 2, 3, 4], 2);
// → [3, 1]

_.shuffle(collection)

#

Creates an array of shuffled values, using a version of the Fisher-Yates shuffle. See http://en.wikipedia.org/wiki/Fisher-Yates_shuffle.

Arguments

  1. collection (Array|Object|string): The collection to shuffle.

Returns

(Array): Returns a new shuffled collection.

Example

_.shuffle([1, 2, 3, 4, 5, 6]);
// → [4, 1, 6, 3, 5, 2]

_.size(collection)

#

Gets the size of the collection by returning collection.length for arrays and array-like objects or the number of own enumerable properties for objects.

Arguments

  1. collection (Array|Object|string): The collection to inspect.

Returns

(number): Returns collection.length or number of own enumerable properties.

Example

_.size([1, 2]);
// → 2

_.size({ 'one': 1, 'two': 2, 'three': 3 });
// → 3

_.size('pebbles');
// → 7

_.some(collection, [callback=identity], [thisArg])

#

Checks if the callback returns a truthy value for **any** element of a collection. The function returns as soon as it finds a passing value and does not iterate over the entire collection. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Aliases

_.any

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(boolean): Returns true if any element passed the callback check, else false.

Example

_.some([null, 0, 'yes', false], Boolean);
// → true

var characters = [
  { 'name': 'barney', 'age': 36, 'blocked': false },
  { 'name': 'fred',   'age': 40, 'blocked': true }
];

// using "_.pluck" callback shorthand
_.some(characters, 'blocked');
// → true

// using "_.where" callback shorthand
_.some(characters, { 'age': 1 });
// → false

_.sortBy(collection, [callback=identity], [thisArg])

#

Creates an array of elements, sorted in ascending order by the results of running each element in a collection through the callback. This method performs a stable sort, that is, it will preserve the original sort order of equal elements. The callback is bound to thisArg and invoked with three arguments; (value, index|key, collection).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an array of property names is provided for callback the collection will be sorted by each property value.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns a new array of sorted elements.

Example

_.sortBy([1, 2, 3], function(num) { return Math.sin(num); });
// → [3, 1, 2]

_.sortBy([1, 2, 3], function(num) { return this.sin(num); }, Math);
// → [3, 1, 2]

var characters = [
  { 'name': 'barney',  'age': 36 },
  { 'name': 'fred',    'age': 40 },
  { 'name': 'barney',  'age': 26 },
  { 'name': 'fred',    'age': 30 }
];

// using "_.pluck" callback shorthand
_.map(_.sortBy(characters, 'age'), _.values);
// → [['barney', 26], ['fred', 30], ['barney', 36], ['fred', 40]]

// sorting by multiple properties
_.map(_.sortBy(characters, ['name', 'age']), _.values);
// = > [['barney', 26], ['barney', 36], ['fred', 30], ['fred', 40]]

_.toArray(collection)

#

Converts the collection to an array.

Arguments

  1. collection (Array|Object|string): The collection to convert.

Returns

(Array): Returns the new converted array.

Example

(function() { return _.toArray(arguments).slice(1); })(1, 2, 3, 4);
// → [2, 3, 4]

_.where(collection, props)

#

Performs a deep comparison of each element in a collection to the given properties object, returning an array of all elements that have equivalent property values.

Arguments

  1. collection (Array|Object|string): The collection to iterate over.
  2. props (Object): The object of property values to filter by.

Returns

(Array): Returns a new array of elements that have the given properties.

Example

var characters = [
  { 'name': 'barney', 'age': 36, 'pets': ['hoppy'] },
  { 'name': 'fred',   'age': 40, 'pets': ['baby puss', 'dino'] }
];

_.where(characters, { 'age': 36 });
// → [{ 'name': 'barney', 'age': 36, 'pets': ['hoppy'] }]

_.where(characters, { 'pets': ['dino'] });
// → [{ 'name': 'fred', 'age': 40, 'pets': ['baby puss', 'dino'] }]

“Functions” Methods

_.after(n, func)

#

Creates a function that executes func, with the this binding and arguments of the created function, only after being called n times.

Arguments

  1. n (number): The number of times the function must be called before func is executed.
  2. func (Function): The function to restrict.

Returns

(Function): Returns the new restricted function.

Example

var saves = ['profile', 'settings'];

var done = _.after(saves.length, function() {
  console.log('Done saving!');
});

_.forEach(saves, function(type) {
  asyncSave({ 'type': type, 'complete': done });
});
// → logs 'Done saving!', after all saves have completed

_.bind(func, [thisArg], [arg])

#

Creates a function that, when called, invokes func with the this binding of thisArg and prepends any additional bind arguments to those provided to the bound function.

Arguments

  1. func (Function): The function to bind.
  2. [thisArg] (*): The this binding of func.
  3. [arg] (…*): Arguments to be partially applied.

Returns

(Function): Returns the new bound function.

Example

var func = function(greeting) {
  return greeting + ' ' + this.name;
};

func = _.bind(func, { 'name': 'fred' }, 'hi');
func();
// → 'hi fred'

_.bindAll(object, [methodName])

#

Binds methods of an object to the object itself, overwriting the existing method. Method names may be specified as individual arguments or as arrays of method names. If no method names are provided all the function properties of object will be bound.

Arguments

  1. object (Object): The object to bind and assign the bound methods to.
  2. [methodName] (…string): The object method names to bind, specified as individual method names or arrays of method names.

Returns

(Object): Returns object.

Example

var view = {
  'label': 'docs',
  'onClick': function() { console.log('clicked ' + this.label); }
};

_.bindAll(view);
jQuery('#docs').on('click', view.onClick);
// → logs 'clicked docs', when the button is clicked

_.bindKey(object, key, [arg])

#

Creates a function that, when called, invokes the method at object[key] and prepends any additional bindKey arguments to those provided to the bound function. This method differs from _.bind by allowing bound functions to reference methods that will be redefined or don't yet exist. See http://michaux.ca/articles/lazy-function-definition-pattern.

Arguments

  1. object (Object): The object the method belongs to.
  2. key (string): The key of the method.
  3. [arg] (…*): Arguments to be partially applied.

Returns

(Function): Returns the new bound function.

Example

var object = {
  'name': 'fred',
  'greet': function(greeting) {
    return greeting + ' ' + this.name;
  }
};

var func = _.bindKey(object, 'greet', 'hi');
func();
// → 'hi fred'

object.greet = function(greeting) {
  return greeting + 'ya ' + this.name + '!';
};

func();
// → 'hiya fred!'

_.compose([func])

#

Creates a function that is the composition of the provided functions, where each function consumes the return value of the function that follows. For example, composing the functions f(), g(), and h() produces f(g(h())). Each function is executed with the this binding of the composed function.

Arguments

  1. [func] (…Function): Functions to compose.

Returns

(Function): Returns the new composed function.

Example

var realNameMap = {
  'pebbles': 'penelope'
};

var format = function(name) {
  name = realNameMap[name.toLowerCase()] || name;
  return name.charAt(0).toUpperCase() + name.slice(1).toLowerCase();
};

var greet = function(formatted) {
  return 'Hiya ' + formatted + '!';
};

var welcome = _.compose(greet, format);
welcome('pebbles');
// → 'Hiya Penelope!'

_.curry(func, [arity=func.length])

#

Creates a function which accepts one or more arguments of func that when invoked either executes func returning its result, if all func arguments have been provided, or returns a function that accepts one or more of the remaining func arguments, and so on. The arity of func can be specified if func.length is not sufficient.

Arguments

  1. func (Function): The function to curry.
  2. [arity=func.length] (number): The arity of func.

Returns

(Function): Returns the new curried function.

Example

var curried = _.curry(function(a, b, c) {
  console.log(a + b + c);
});

curried(1)(2)(3);
// → 6

curried(1, 2)(3);
// → 6

curried(1, 2, 3);
// → 6

_.debounce(func, wait, [options])

#

Creates a function that will delay the execution of func until after wait milliseconds have elapsed since the last time it was invoked. Provide an options object to indicate that func should be invoked on the leading and/or trailing edge of the wait timeout. Subsequent calls to the debounced function will return the result of the last func call.

Note: If leading and trailing options are true func will be called on the trailing edge of the timeout only if the the debounced function is invoked more than once during the wait timeout.

Arguments

  1. func (Function): The function to debounce.
  2. wait (number): The number of milliseconds to delay.
  3. [options] (Object): The options object.
  4. [options.leading=false] (boolean): Specify execution on the leading edge of the timeout.
  5. [options.maxWait] (number): The maximum time func is allowed to be delayed before it’s called.
  6. [options.trailing=true] (boolean): Specify execution on the trailing edge of the timeout.

Returns

(Function): Returns the new debounced function.

Example

// avoid costly calculations while the window size is in flux
var lazyLayout = _.debounce(calculateLayout, 150);
jQuery(window).on('resize', lazyLayout);

// execute `sendMail` when the click event is fired, debouncing subsequent calls
jQuery('#postbox').on('click', _.debounce(sendMail, 300, {
  'leading': true,
  'trailing': false
});

// ensure `batchLog` is executed once after 1 second of debounced calls
var source = new EventSource('/stream');
source.addEventListener('message', _.debounce(batchLog, 250, {
  'maxWait': 1000
}, false);

_.defer(func, [arg])

#

Defers executing the func function until the current call stack has cleared. Additional arguments will be provided to func when it is invoked.

Arguments

  1. func (Function): The function to defer.
  2. [arg] (…*): Arguments to invoke the function with.

Returns

(number): Returns the timer id.

Example

_.defer(function(text) { console.log(text); }, 'deferred');
// logs 'deferred' after one or more milliseconds

_.delay(func, wait, [arg])

#

Executes the func function after wait milliseconds. Additional arguments will be provided to func when it is invoked.

Arguments

  1. func (Function): The function to delay.
  2. wait (number): The number of milliseconds to delay execution.
  3. [arg] (…*): Arguments to invoke the function with.

Returns

(number): Returns the timer id.

Example

_.delay(function(text) { console.log(text); }, 1000, 'later');
// → logs 'later' after one second

_.memoize(func, [resolver])

#

Creates a function that memoizes the result of func. If resolver is provided it will be used to determine the cache key for storing the result based on the arguments provided to the memoized function. By default, the first argument provided to the memoized function is used as the cache key. The func is executed with the this binding of the memoized function. The result cache is exposed as the cache property on the memoized function.

Arguments

  1. func (Function): The function to have its output memoized.
  2. [resolver] (Function): A function used to resolve the cache key.

Returns

(Function): Returns the new memoizing function.

Example

var fibonacci = _.memoize(function(n) {
  return n < 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
});

fibonacci(9)
// → 34

var data = {
  'fred': { 'name': 'fred', 'age': 40 },
  'pebbles': { 'name': 'pebbles', 'age': 1 }
};

// modifying the result cache
var get = _.memoize(function(name) { return data[name]; }, _.identity);
get('pebbles');
// → { 'name': 'pebbles', 'age': 1 }

get.cache.pebbles.name = 'penelope';
get('pebbles');
// → { 'name': 'penelope', 'age': 1 }

_.once(func)

#

Creates a function that is restricted to execute func once. Repeat calls to the function will return the value of the first call. The func is executed with the this binding of the created function.

Arguments

  1. func (Function): The function to restrict.

Returns

(Function): Returns the new restricted function.

Example

var initialize = _.once(createApplication);
initialize();
initialize();
// `initialize` executes `createApplication` once

_.partial(func, [arg])

#

Creates a function that, when called, invokes func with any additional partial arguments prepended to those provided to the new function. This method is similar to _.bind except it does **not** alter the this binding.

Arguments

  1. func (Function): The function to partially apply arguments to.
  2. [arg] (…*): Arguments to be partially applied.

Returns

(Function): Returns the new partially applied function.

Example

var greet = function(greeting, name) { return greeting + ' ' + name; };
var hi = _.partial(greet, 'hi');
hi('fred');
// → 'hi fred'

_.partialRight(func, [arg])

#

This method is like _.partial except that partial arguments are appended to those provided to the new function.

Arguments

  1. func (Function): The function to partially apply arguments to.
  2. [arg] (…*): Arguments to be partially applied.

Returns

(Function): Returns the new partially applied function.

Example

var defaultsDeep = _.partialRight(_.merge, function deep(value, other) {
  return _.merge(value, other, deep);
});

var options = {
  'variable': 'data',
  'imports': { 'jq': $ }
};

defaultsDeep(options, _.templateSettings);

options.variable
// → 'data'

options.imports
// → { '_': _, 'jq': $ }

_.throttle(func, wait, [options])

#

Creates a function that, when executed, will only call the func function at most once per every wait milliseconds. Provide an options object to indicate that func should be invoked on the leading and/or trailing edge of the wait timeout. Subsequent calls to the throttled function will return the result of the last func call.

Note: If leading and trailing options are true func will be called on the trailing edge of the timeout only if the the throttled function is invoked more than once during the wait timeout.

Arguments

  1. func (Function): The function to throttle.
  2. wait (number): The number of milliseconds to throttle executions to.
  3. [options] (Object): The options object.
  4. [options.leading=true] (boolean): Specify execution on the leading edge of the timeout.
  5. [options.trailing=true] (boolean): Specify execution on the trailing edge of the timeout.

Returns

(Function): Returns the new throttled function.

Example

// avoid excessively updating the position while scrolling
var throttled = _.throttle(updatePosition, 100);
jQuery(window).on('scroll', throttled);

// execute `renewToken` when the click event is fired, but not more than once every 5 minutes
jQuery('.interactive').on('click', _.throttle(renewToken, 300000, {
  'trailing': false
}));

_.wrap(value, wrapper)

#

Creates a function that provides value to the wrapper function as its first argument. Additional arguments provided to the function are appended to those provided to the wrapper function. The wrapper is executed with the this binding of the created function.

Arguments

  1. value (*): The value to wrap.
  2. wrapper (Function): The wrapper function.

Returns

(Function): Returns the new function.

Example

var p = _.wrap(_.escape, function(func, text) {
  return '<p>' + func(text) + '<p>';
});

p('Fred, Wilma, & Pebbles');
// → '<p>Fred, Wilma, &amp; Pebbles<p>'

“Objects” Methods

_.assign(object, [source], [callback], [thisArg])

#

Assigns own enumerable properties of source object(s) to the destination object. Subsequent sources will overwrite property assignments of previous sources. If a callback is provided it will be executed to produce the assigned values. The callback is bound to thisArg and invoked with two arguments; (objectValue, sourceValue).

Aliases

_.extend

Arguments

  1. object (Object): The destination object.
  2. [source] (…Object): The source objects.
  3. [callback] (Function): The function to customize assigning values.
  4. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns the destination object.

Example

_.assign({ 'name': 'fred' }, { 'employer': 'slate' });
// → { 'name': 'fred', 'employer': 'slate' }

var defaults = _.partialRight(_.assign, function(a, b) {
  return typeof a == 'undefined' ? b : a;
});

var object = { 'name': 'barney' };
defaults(object, { 'name': 'fred', 'employer': 'slate' });
// → { 'name': 'barney', 'employer': 'slate' }

_.clone(value, [isDeep=false], [callback], [thisArg])

#

Creates a clone of value. If isDeep is true nested objects will also be cloned, otherwise they will be assigned by reference. If a callback is provided it will be executed to produce the cloned values. If the callback returns undefined cloning will be handled by the method instead. The callback is bound to thisArg and invoked with one argument; (value).

Arguments

  1. value (*): The value to clone.
  2. [isDeep=false] (boolean): Specify a deep clone.
  3. [callback] (Function): The function to customize cloning values.
  4. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the cloned value.

Example

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

var shallow = _.clone(characters);
shallow[0] === characters[0];
// → true

var deep = _.clone(characters, true);
deep[0] === characters[0];
// → false

_.mixin({
  'clone': _.partialRight(_.clone, function(value) {
    return _.isElement(value) ? value.cloneNode(false) : undefined;
  })
});

var clone = _.clone(document.body);
clone.childNodes.length;
// → 0

_.cloneDeep(value, [callback], [thisArg])

#

Creates a deep clone of value. If a callback is provided it will be executed to produce the cloned values. If the callback returns undefined cloning will be handled by the method instead. The callback is bound to thisArg and invoked with one argument; (value).

Note: This method is loosely based on the structured clone algorithm. Functions and DOM nodes are **not** cloned. The enumerable properties of arguments objects and objects created by constructors other than Object are cloned to plain Object objects. See http://www.w3.org/TR/html5/infrastructure.html#internal-structured-cloning-algorithm.

Arguments

  1. value (*): The value to deep clone.
  2. [callback] (Function): The function to customize cloning values.
  3. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the deep cloned value.

Example

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

var deep = _.cloneDeep(characters);
deep[0] === characters[0];
// → false

var view = {
  'label': 'docs',
  'node': element
};

var clone = _.cloneDeep(view, function(value) {
  return _.isElement(value) ? value.cloneNode(true) : undefined;
});

clone.node == view.node;
// → false

_.create(prototype, [properties])

#

Creates an object that inherits from the given prototype object. If a properties object is provided its own enumerable properties are assigned to the created object.

Arguments

  1. prototype (Object): The object to inherit from.
  2. [properties] (Object): The properties to assign to the object.

Returns

(Object): Returns the new object.

Example

function Shape() {
  this.x = 0;
  this.y = 0;
}

function Circle() {
  Shape.call(this);
}

Circle.prototype = _.create(Shape.prototype, { 'constructor': Circle });

var circle = new Circle;
circle instanceof Circle;
// → true

circle instanceof Shape;
// → true

_.defaults(object, [source])

#

Assigns own enumerable properties of source object(s) to the destination object for all destination properties that resolve to undefined. Once a property is set, additional defaults of the same property will be ignored.

Arguments

  1. object (Object): The destination object.
  2. [source] (…Object): The source objects.

Returns

(Object): Returns the destination object.

Example

var object = { 'name': 'barney' };
_.defaults(object, { 'name': 'fred', 'employer': 'slate' });
// → { 'name': 'barney', 'employer': 'slate' }

_.findKey(object, [callback=identity], [thisArg])

#

This method is like _.findIndex except that it returns the key of the first element that passes the callback check, instead of the element itself.

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. object (Object): The object to search.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(string, undefined): Returns the key of the found element, else undefined.

Example

var characters = {
  'barney': {  'age': 36, 'blocked': false },
  'fred': {    'age': 40, 'blocked': true },
  'pebbles': { 'age': 1,  'blocked': false }
};

_.findKey(characters, function(chr) {
  return chr.age < 40;
});
// → 'barney' (property order is not guaranteed across environments)

// using "_.where" callback shorthand
_.findKey(characters, { 'age': 1 });
// → 'pebbles'

// using "_.pluck" callback shorthand
_.findKey(characters, 'blocked');
// → 'fred'

_.findLastKey(object, [callback=identity], [thisArg])

#

This method is like _.findKey except that it iterates over elements of a collection in the opposite order.

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. object (Object): The object to search.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(string, undefined): Returns the key of the found element, else undefined.

Example

var characters = {
  'barney': {  'age': 36, 'blocked': true },
  'fred': {    'age': 40, 'blocked': false },
  'pebbles': { 'age': 1,  'blocked': true }
};

_.findLastKey(characters, function(chr) {
  return chr.age < 40;
});
// → returns `pebbles`, assuming `_.findKey` returns `barney`

// using "_.where" callback shorthand
_.findLastKey(characters, { 'age': 40 });
// → 'fred'

// using "_.pluck" callback shorthand
_.findLastKey(characters, 'blocked');
// → 'pebbles'

_.forIn(object, [callback=identity], [thisArg])

#

Iterates over own and inherited enumerable properties of an object, executing the callback for each property. The callback is bound to thisArg and invoked with three arguments; (value, key, object). Callbacks may exit iteration early by explicitly returning false.

Arguments

  1. object (Object): The object to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns object.

Example

function Shape() {
  this.x = 0;
  this.y = 0;
}

Shape.prototype.move = function(x, y) {
  this.x += x;
  this.y += y;
};

_.forIn(new Shape, function(value, key) {
  console.log(key);
});
// → logs 'x', 'y', and 'move' (property order is not guaranteed across environments)

_.forInRight(object, [callback=identity], [thisArg])

#

This method is like _.forIn except that it iterates over elements of a collection in the opposite order.

Arguments

  1. object (Object): The object to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns object.

Example

function Shape() {
  this.x = 0;
  this.y = 0;
}

Shape.prototype.move = function(x, y) {
  this.x += x;
  this.y += y;
};

_.forInRight(new Shape, function(value, key) {
  console.log(key);
});
// → logs 'move', 'y', and 'x' assuming `_.forIn ` logs 'x', 'y', and 'move'

_.forOwn(object, [callback=identity], [thisArg])

#

Iterates over own enumerable properties of an object, executing the callback for each property. The callback is bound to thisArg and invoked with three arguments; (value, key, object). Callbacks may exit iteration early by explicitly returning false.

Arguments

  1. object (Object): The object to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns object.

Example

_.forOwn({ '0': 'zero', '1': 'one', 'length': 2 }, function(num, key) {
  console.log(key);
});
// → logs '0', '1', and 'length' (property order is not guaranteed across environments)

_.forOwnRight(object, [callback=identity], [thisArg])

#

This method is like _.forOwn except that it iterates over elements of a collection in the opposite order.

Arguments

  1. object (Object): The object to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns object.

Example

_.forOwnRight({ '0': 'zero', '1': 'one', 'length': 2 }, function(num, key) {
  console.log(key);
});
// → logs 'length', '1', and '0' assuming `_.forOwn` logs '0', '1', and 'length'

_.functions(object)

#

Creates a sorted array of property names of all enumerable properties, own and inherited, of object that have function values.

Aliases

_.methods

Arguments

  1. object (Object): The object to inspect.

Returns

(Array): Returns an array of property names that have function values.

Example

_.functions(_);
// → ['all', 'any', 'bind', 'bindAll', 'clone', 'compact', 'compose', …]

_.has(object, key)

#

Checks if the specified property name exists as a direct property of object, instead of an inherited property.

Arguments

  1. object (Object): The object to inspect.
  2. key (string): The name of the property to check.

Returns

(boolean): Returns true if key is a direct property, else false.

Example

_.has({ 'a': 1, 'b': 2, 'c': 3 }, 'b');
// → true

_.invert(object)

#

Creates an object composed of the inverted keys and values of the given object.

Arguments

  1. object (Object): The object to invert.

Returns

(Object): Returns the created inverted object.

Example

_.invert({ 'first': 'fred', 'second': 'barney' });
// → { 'fred': 'first', 'barney': 'second' }

_.isArguments(value)

#

Checks if value is an arguments object.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is an arguments object, else false.

Example

(function() { return _.isArguments(arguments); })(1, 2, 3);
// → true

_.isArguments([1, 2, 3]);
// → false

_.isArray(value)

#

Checks if value is an array.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is an array, else false.

Example

(function() { return _.isArray(arguments); })();
// → false

_.isArray([1, 2, 3]);
// → true

_.isBoolean(value)

#

Checks if value is a boolean value.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is a boolean value, else false.

Example

_.isBoolean(null);
// → false

_.isDate(value)

#

Checks if value is a date.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is a date, else false.

Example

_.isDate(new Date);
// → true

_.isElement(value)

#

Checks if value is a DOM element.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is a DOM element, else false.

Example

_.isElement(document.body);
// → true

_.isEmpty(value)

#

Checks if value is empty. Arrays, strings, or arguments objects with a length of 0 and objects with no own enumerable properties are considered "empty".

Arguments

  1. value (Array|Object|string): The value to inspect.

Returns

(boolean): Returns true if the value is empty, else false.

Example

_.isEmpty([1, 2, 3]);
// → false

_.isEmpty({});
// → true

_.isEmpty('');
// → true

_.isEqual(a, b, [callback], [thisArg])

#

Performs a deep comparison between two values to determine if they are equivalent to each other. If a callback is provided it will be executed to compare values. If the callback returns undefined comparisons will be handled by the method instead. The callback is bound to thisArg and invoked with two arguments; (a, b).

Arguments

  1. a (*): The value to compare.
  2. b (*): The other value to compare.
  3. [callback] (Function): The function to customize comparing values.
  4. [thisArg] (*): The this binding of callback.

Returns

(boolean): Returns true if the values are equivalent, else false.

Example

var object = { 'name': 'fred' };
var copy = { 'name': 'fred' };

object == copy;
// → false

_.isEqual(object, copy);
// → true

var words = ['hello', 'goodbye'];
var otherWords = ['hi', 'goodbye'];

_.isEqual(words, otherWords, function(a, b) {
  var reGreet = /^(?:hello|hi)$/i,
      aGreet = _.isString(a) && reGreet.test(a),
      bGreet = _.isString(b) && reGreet.test(b);

  return (aGreet || bGreet) ? (aGreet == bGreet) : undefined;
});
// → true

_.isFinite(value)

#

Checks if value is, or can be coerced to, a finite number.

Note: This is not the same as native isFinite which will return true for booleans and empty strings. See http://es5.github.io/#x15.1.2.5.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is finite, else false.

Example

_.isFinite(-101);
// → true

_.isFinite('10');
// → true

_.isFinite(true);
// → false

_.isFinite('');
// → false

_.isFinite(Infinity);
// → false

_.isFunction(value)

#

Checks if value is a function.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is a function, else false.

Example

_.isFunction(_);
// → true

_.isNaN(value)

#

Checks if value is NaN.

Note: This is not the same as native isNaN which will return true for undefined and other non-numeric values. See http://es5.github.io/#x15.1.2.4.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is NaN, else false.

Example

_.isNaN(NaN);
// → true

_.isNaN(new Number(NaN));
// → true

isNaN(undefined);
// → true

_.isNaN(undefined);
// → false

_.isNull(value)

#

Checks if value is null.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is null, else false.

Example

_.isNull(null);
// → true

_.isNull(undefined);
// → false

_.isNumber(value)

#

Checks if value is a number.

Note: NaN is considered a number. See http://es5.github.io/#x8.5.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is a number, else false.

Example

_.isNumber(8.4 * 5);
// → true

_.isObject(value)

#

Checks if value is the language type of Object. (e.g. arrays, functions, objects, regexes, new Number(0), and new String(''))

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is an object, else false.

Example

_.isObject({});
// → true

_.isObject([1, 2, 3]);
// → true

_.isObject(1);
// → false

_.isPlainObject(value)

#

Checks if value is an object created by the Object constructor.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if value is a plain object, else false.

Example

function Shape() {
  this.x = 0;
  this.y = 0;
}

_.isPlainObject(new Shape);
// → false

_.isPlainObject([1, 2, 3]);
// → false

_.isPlainObject({ 'x': 0, 'y': 0 });
// → true

_.isRegExp(value)

#

Checks if value is a regular expression.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is a regular expression, else false.

Example

_.isRegExp(/fred/);
// → true

_.isString(value)

#

Checks if value is a string.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is a string, else false.

Example

_.isString('fred');
// → true

_.isUndefined(value)

#

Checks if value is undefined.

Arguments

  1. value (*): The value to check.

Returns

(boolean): Returns true if the value is undefined, else false.

Example

_.isUndefined(void 0);
// → true

_.keys(object)

#

Creates an array composed of the own enumerable property names of an object.

Arguments

  1. object (Object): The object to inspect.

Returns

(Array): Returns an array of property names.

Example

_.keys({ 'one': 1, 'two': 2, 'three': 3 });
// → ['one', 'two', 'three'] (property order is not guaranteed across environments)

_.mapValues(object, [callback=identity], [thisArg])

#

Creates an object with the same keys as object and values generated by running each own enumerable property of object through the callback. The callback is bound to thisArg and invoked with three arguments; (value, key, object).

If a property name is provided for callback the created "_.pluck" style callback will return the property value of the given element.

If an object is provided for callback the created "_.where" style callback will return true for elements that have the properties of the given object, else false.

Arguments

  1. object (Object): The object to iterate over.
  2. [callback=identity] (Function|Object|string): The function called per iteration. If a property name or object is provided it will be used to create a ".pluck" or ".where" style callback, respectively.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns a new object with values of the results of each callback execution.

Example

_.mapValues({ 'a': 1, 'b': 2, 'c': 3} , function(num) { return num * 3; });
// → { 'a': 3, 'b': 6, 'c': 9 }

var characters = {
  'fred': { 'name': 'fred', 'age': 40 },
  'pebbles': { 'name': 'pebbles', 'age': 1 }
};

// using "_.pluck" callback shorthand
_.mapValues(characters, 'age');
// → { 'fred': 40, 'pebbles': 1 }

_.merge(object, [source], [callback], [thisArg])

#

Recursively merges own enumerable properties of the source object(s), that don't resolve to undefined into the destination object. Subsequent sources will overwrite property assignments of previous sources. If a callback is provided it will be executed to produce the merged values of the destination and source properties. If the callback returns undefined merging will be handled by the method instead. The callback is bound to thisArg and invoked with two arguments; (objectValue, sourceValue).

Arguments

  1. object (Object): The destination object.
  2. [source] (…Object): The source objects.
  3. [callback] (Function): The function to customize merging properties.
  4. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns the destination object.

Example

var names = {
  'characters': [
    { 'name': 'barney' },
    { 'name': 'fred' }
  ]
};

var ages = {
  'characters': [
    { 'age': 36 },
    { 'age': 40 }
  ]
};

_.merge(names, ages);
// → { 'characters': [{ 'name': 'barney', 'age': 36 }, { 'name': 'fred', 'age': 40 }] }

var food = {
  'fruits': ['apple'],
  'vegetables': ['beet']
};

var otherFood = {
  'fruits': ['banana'],
  'vegetables': ['carrot']
};

_.merge(food, otherFood, function(a, b) {
  return _.isArray(a) ? a.concat(b) : undefined;
});
// → { 'fruits': ['apple', 'banana'], 'vegetables': ['beet', 'carrot] }

_.omit(object, [callback], [thisArg])

#

Creates a shallow clone of object excluding the specified properties. Property names may be specified as individual arguments or as arrays of property names. If a callback is provided it will be executed for each property of object omitting the properties the callback returns truthy for. The callback is bound to thisArg and invoked with three arguments; (value, key, object).

Arguments

  1. object (Object): The source object.
  2. [callback] (Function|…string|string[]): The properties to omit or the function called per iteration.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns an object without the omitted properties.

Example

_.omit({ 'name': 'fred', 'age': 40 }, 'age');
// → { 'name': 'fred' }

_.omit({ 'name': 'fred', 'age': 40 }, function(value) {
  return typeof value == 'number';
});
// → { 'name': 'fred' }

_.pairs(object)

#

Creates a two dimensional array of an object’s key-value pairs, i.e. [[key1, value1], [key2, value2]].

Arguments

  1. object (Object): The object to inspect.

Returns

(Array): Returns new array of key-value pairs.

Example

_.pairs({ 'barney': 36, 'fred': 40 });
// → [['barney', 36], ['fred', 40]] (property order is not guaranteed across environments)

_.pick(object, [callback], [thisArg])

#

Creates a shallow clone of object composed of the specified properties. Property names may be specified as individual arguments or as arrays of property names. If a callback is provided it will be executed for each property of object picking the properties the callback returns truthy for. The callback is bound to thisArg and invoked with three arguments; (value, key, object).

Arguments

  1. object (Object): The source object.
  2. [callback] (Function|…string|string[]): The function called per iteration or property names to pick, specified as individual property names or arrays of property names.
  3. [thisArg] (*): The this binding of callback.

Returns

(Object): Returns an object composed of the picked properties.

Example

_.pick({ 'name': 'fred', '_userid': 'fred1' }, 'name');
// → { 'name': 'fred' }

_.pick({ 'name': 'fred', '_userid': 'fred1' }, function(value, key) {
  return key.charAt(0) != '_';
});
// → { 'name': 'fred' }

_.transform(object, [callback=identity], [accumulator], [thisArg])

#

An alternative to _.reduce this method transforms object to a new accumulator object which is the result of running each of its own enumerable properties through a callback, with each callback execution potentially mutating the accumulator object. The callback is bound to thisArg and invoked with four arguments; (accumulator, value, key, object). Callbacks may exit iteration early by explicitly returning false.

Arguments

  1. object (Array|Object): The object to iterate over.
  2. [callback=identity] (Function): The function called per iteration.
  3. [accumulator] (*): The custom accumulator value.
  4. [thisArg] (*): The this binding of callback.

Returns

(*): Returns the accumulated value.

Example

var squares = _.transform([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], function(result, num) {
  num *= num;
  if (num % 2) {
    return result.push(num) < 3;
  }
});
// → [1, 9, 25]

var mapped = _.transform({ 'a': 1, 'b': 2, 'c': 3 }, function(result, num, key) {
  result[key] = num * 3;
});
// → { 'a': 3, 'b': 6, 'c': 9 }

_.values(object)

#

Creates an array composed of the own enumerable property values of object.

Arguments

  1. object (Object): The object to inspect.

Returns

(Array): Returns an array of property values.

Example

_.values({ 'one': 1, 'two': 2, 'three': 3 });
// → [1, 2, 3] (property order is not guaranteed across environments)

“Utilities” Methods

_.now

#

(unknown): Gets the number of milliseconds that have elapsed since the Unix epoch (1 January 1970 00:00:00 UTC).

Example

var stamp = _.now();
_.defer(function() { console.log(_.now() - stamp); });
// → logs the number of milliseconds it took for the deferred function to be called

_.constant(value)

#

Creates a function that returns value.

Arguments

  1. value (*): The value to return from the new function.

Returns

(Function): Returns the new function.

Example

var object = { 'name': 'fred' };
var getter = _.constant(object);
getter() === object;
// → true

_.createCallback([func=identity], [thisArg], [argCount])

#

Produces a callback bound to an optional thisArg. If func is a property name the created callback will return the property value for a given element. If func is an object the created callback will return true for elements that contain the equivalent object properties, otherwise it will return false.

Arguments

  1. [func=identity] (*): The value to convert to a callback.
  2. [thisArg] (*): The this binding of the created callback.
  3. [argCount] (number): The number of arguments the callback accepts.

Returns

(Function): Returns a callback function.

Example

var characters = [
  { 'name': 'barney', 'age': 36 },
  { 'name': 'fred',   'age': 40 }
];

// wrap to create custom callback shorthands
_.createCallback = _.wrap(_.createCallback, function(func, callback, thisArg) {
  var match = /^(.+?)__([gl]t)(.+)$/.exec(callback);
  return !match ? func(callback, thisArg) : function(object) {
    return match[2] == 'gt' ? object[match[1]] > match[3] : object[match[1]] < match[3];
  };
});

_.filter(characters, 'age__gt38');
// → [{ 'name': 'fred', 'age': 40 }]

_.escape(string)

#

Converts the characters &, <, >, ", and ' in string to their corresponding HTML entities.

Arguments

  1. string (string): The string to escape.

Returns

(string): Returns the escaped string.

Example

_.escape('Fred, Wilma, & Pebbles');
// → 'Fred, Wilma, &amp; Pebbles'

_.identity(value)

#

This method returns the first argument provided to it.

Arguments

  1. value (*): Any value.

Returns

(*): Returns value.

Example

var object = { 'name': 'fred' };
_.identity(object) === object;
// → true

_.mixin([object=lodash], source, [options])

#

Adds function properties of a source object to the destination object. If object is a function methods will be added to its prototype as well.

Arguments

  1. [object=lodash] (Function|Object): object The destination object.
  2. source (Object): The object of functions to add.
  3. [options] (Object): The options object.
  4. [options.chain=true] (boolean): Specify whether the functions added are chainable.

Example

function capitalize(string) {
  return string.charAt(0).toUpperCase() + string.slice(1).toLowerCase();
}

_.mixin({ 'capitalize': capitalize });
_.capitalize('fred');
// → 'Fred'

_('fred').capitalize().value();
// → 'Fred'

_.mixin({ 'capitalize': capitalize }, { 'chain': false });
_('fred').capitalize();
// → 'Fred'

_.noConflict()

#

Reverts the '_' variable to its previous value and returns a reference to the lodash function.

Returns

(Function): Returns the lodash function.

Example

var lodash = _.noConflict();

_.noop()

#

A no-operation function.

Example

var object = { 'name': 'fred' };
_.noop(object) === undefined;
// → true

_.parseInt(value, [radix])

#

Converts the given value into an integer of the specified radix. If radix is undefined or 0 a radix of 10 is used unless the value is a hexadecimal, in which case a radix of 16 is used.

Note: This method avoids differences in native ES3 and ES5 parseInt implementations. See http://es5.github.io/#E.

Arguments

  1. value (string): The value to parse.
  2. [radix] (number): The radix used to interpret the value to parse.

Returns

(number): Returns the new integer value.

Example

_.parseInt('08');
// → 8

_.property(key)

#

Creates a "_.pluck" style function, which returns the key value of a given object.

Arguments

  1. key (string): The name of the property to retrieve.

Returns

(Function): Returns the new function.

Example

var characters = [
  { 'name': 'fred',   'age': 40 },
  { 'name': 'barney', 'age': 36 }
];

var getName = _.property('name');

_.map(characters, getName);
// → ['barney', 'fred']

_.sortBy(characters, getName);
// → [{ 'name': 'barney', 'age': 36 }, { 'name': 'fred',   'age': 40 }]

_.random([min=0], [max=1], [floating=false])

#

Produces a random number between min and max (inclusive). If only one argument is provided a number between 0 and the given number will be returned. If floating is truthy or either min or max are floats a floating-point number will be returned instead of an integer.

Arguments

  1. [min=0] (number): The minimum possible value.
  2. [max=1] (number): The maximum possible value.
  3. [floating=false] (boolean): Specify returning a floating-point number.

Returns

(number): Returns a random number.

Example

_.random(0, 5);
// → an integer between 0 and 5

_.random(5);
// → also an integer between 0 and 5

_.random(5, true);
// → a floating-point number between 0 and 5

_.random(1.2, 5.2);
// → a floating-point number between 1.2 and 5.2

_.result(object, key)

#

Resolves the value of property key on object. If key is a function it will be invoked with the this binding of object and its result returned, else the property value is returned. If object is falsey then undefined is returned.

Arguments

  1. object (Object): The object to inspect.
  2. key (string): The name of the property to resolve.

Returns

(*): Returns the resolved value.

Example

var object = {
  'cheese': 'crumpets',
  'stuff': function() {
    return 'nonsense';
  }
};

_.result(object, 'cheese');
// → 'crumpets'

_.result(object, 'stuff');
// → 'nonsense'

_.runInContext([context=root])

#

Create a new lodash function using the given context object.

Arguments

  1. [context=root] (Object): The context object.

Returns

(Function): Returns the lodash function.


_.template(text, data, [options])

#

A micro-templating method that handles arbitrary delimiters, preserves whitespace, and correctly escapes quotes within interpolated code.

Note: In the development build, _.template utilizes sourceURLs for easier debugging. See http://www.html5rocks.com/en/tutorials/developertools/sourcemaps/#toc-sourceurl

For more information on precompiling templates see:
http://lodash.com/custom-builds

For more information on Chrome extension sandboxes see:
http://developer.chrome.com/stable/extensions/sandboxingEval.html

Arguments

  1. text (string): The template text.
  2. data (Object): The data object used to populate the text.
  3. [options] (Object): The options object.
  4. [options.escape] (RegExp): The "escape" delimiter.
  5. [options.evaluate] (RegExp): The "evaluate" delimiter.
  6. [options.imports] (Object): An object to import into the template as local variables.
  7. [options.interpolate] (RegExp): The "interpolate" delimiter.
  8. [options.sourceURL] (string): The sourceURL of the template’s compiled source.
  9. [options.variable] (string): The data object variable name.

Returns

(Function, string): Returns a compiled function when no data object is given, else it returns the interpolated text.

Example

// using the "interpolate" delimiter to create a compiled template
var compiled = _.template('hello <%= name %>');
compiled({ 'name': 'fred' });
// → 'hello fred'

// using the "escape" delimiter to escape HTML in data property values
_.template('<b><%- value %></b>', { 'value': '<script>' });
// → '<b>&lt;script&gt;</b>'

// using the "evaluate" delimiter to generate HTML
var list = '<% _.forEach(people, function(name) { %><li><%- name %></li><% }); %>';
_.template(list, { 'people': ['fred', 'barney'] });
// → '<li>fred</li><li>barney</li>'

// using the ES6 delimiter as an alternative to the default "interpolate" delimiter
_.template('hello ${ name }', { 'name': 'pebbles' });
// → 'hello pebbles'

// using the internal `print` function in "evaluate" delimiters
_.template('<% print("hello " + name); %>!', { 'name': 'barney' });
// → 'hello barney!'

// using a custom template delimiters
_.templateSettings.interpolate = /{{([\s\S]+?)}}/g;
_.template('hello {{ name }}!', { 'name': 'mustache' });
// → 'hello mustache!'

// using the `imports` option to import jQuery
var list = '<% jq.each(people, function(name) { %><li><%- name %></li><% }); %>';
_.template(list, { 'people': ['fred', 'barney'] }, { 'imports': { 'jq': jQuery } });
// → '<li>fred</li><li>barney</li>'

// using the `sourceURL` option to specify a custom sourceURL for the template
var compiled = _.template('hello <%= name %>', null, { 'sourceURL': '/basic/greeting.jst' });
compiled(data);
// → find the source of "greeting.jst" under the Sources tab or Resources panel of the web inspector

// using the `variable` option to ensure a with-statement isn't used in the compiled template
var compiled = _.template('hi <%= data.name %>!', null, { 'variable': 'data' });
compiled.source;
// → function(data) {
  var __t, __p = '', __e = _.escape;
  __p += 'hi ' + ((__t = ( data.name )) == null ? '' : __t) + '!';
  return __p;
}

// using the `source` property to inline compiled templates for meaningful
// line numbers in error messages and a stack trace
fs.writeFileSync(path.join(cwd, 'jst.js'), '\
  var JST = {\
    "main": '
+ _.template(mainText).source + '\
  };\
'
);

_.times(n, callback, [thisArg])

#

Executes the callback n times, returning an array of the results of each callback execution. The callback is bound to thisArg and invoked with one argument; (index).

Arguments

  1. n (number): The number of times to execute the callback.
  2. callback (Function): The function called per iteration.
  3. [thisArg] (*): The this binding of callback.

Returns

(Array): Returns an array of the results of each callback execution.

Example

var diceRolls = _.times(3, _.partial(_.random, 1, 6));
// → [3, 6, 4]

_.times(3, function(n) { mage.castSpell(n); });
// → calls `mage.castSpell(n)` three times, passing `n` of `0`, `1`, and `2` respectively

_.times(3, function(n) { this.cast(n); }, mage);
// → also calls `mage.castSpell(n)` three times

_.unescape(string)

#

The inverse of _.escape this method converts the HTML entities &amp;, &lt;, &gt;, &quot;, and &#39; in string to their corresponding characters.

Arguments

  1. string (string): The string to unescape.

Returns

(string): Returns the unescaped string.

Example

_.unescape('Fred, Barney &amp; Pebbles');
// → 'Fred, Barney & Pebbles'

_.uniqueId([prefix])

#

Generates a unique ID. If prefix is provided the ID will be appended to it.

Arguments

  1. [prefix] (string): The value to prefix the ID with.

Returns

(string): Returns the unique ID.

Example

_.uniqueId('contact_');
// → 'contact_104'

_.uniqueId();
// → '105'

Methods

_.templateSettings.imports._

#

A reference to the lodash function.


Properties

_.VERSION

#

(string): The semantic version number.


_.support

#

(Object): An object used to flag environments features.


_.support.argsClass

#

(boolean): Detect if an arguments object’s [[Class]] is resolvable (all but Firefox < 4, IE < 9).


_.support.argsObject

#

(boolean): Detect if arguments objects are Object objects (all but Narwhal and Opera < 10.5).


_.support.enumErrorProps

#

(boolean): Detect if name or message properties of Error.prototype are enumerable by default. (IE < 9, Safari < 5.1)


_.support.enumPrototypes

#

(boolean): Detect if prototype properties are enumerable by default.

Firefox < 3.6, Opera > 9.50 - Opera < 11.60, and Safari < 5.1 (if the prototype or a property on the prototype has been set) incorrectly sets a function’s prototype property [[Enumerable]] value to true.


_.support.funcDecomp

#

(boolean): Detect if functions can be decompiled by Function#toString (all but PS3 and older Opera mobile browsers & avoided in Windows 8 apps).


_.support.funcNames

#

(boolean): Detect if Function#name is supported (all but IE).


_.support.nonEnumArgs

#

(boolean): Detect if arguments object indexes are non-enumerable (Firefox < 4, IE < 9, PhantomJS, Safari < 5.1).


_.support.nonEnumShadows

#

(boolean): Detect if properties shadowing those on Object.prototype are non-enumerable.

In IE < 9 an objects own properties, shadowing non-enumerable ones, are made non-enumerable as well (a.k.a the JScript [[DontEnum]] bug).


_.support.ownLast

#

(boolean): Detect if own properties are iterated after inherited properties (all but IE < 9).


_.support.spliceObjects

#

(boolean): Detect if Array#shift and Array#splice augment array-like objects correctly.

Firefox < 10, IE compatibility mode, and IE < 9 have buggy Array shift() and splice() functions that fail to remove the last element, value[0], of array-like objects even though the length property is set to 0. The shift() method is buggy in IE 8 compatibility mode, while splice() is buggy regardless of mode in IE < 9 and buggy in compatibility mode in IE 9.


_.support.unindexedChars

#

(boolean): Detect lack of support for accessing string characters by index.

IE < 8 can't access characters by index and IE 8 can only access characters by index on string literals.


_.templateSettings

#

(Object): By default, the template delimiters used by Lo-Dash are similar to those in embedded Ruby (ERB). Change the following template settings to use alternative delimiters.


_.templateSettings.escape

#

(RegExp): Used to detect data property values to be HTML-escaped.


_.templateSettings.evaluate

#

(RegExp): Used to detect code to be evaluated.


_.templateSettings.interpolate

#

(RegExp): Used to detect data property values to inject.


_.templateSettings.variable

#

(string): Used to reference the data object in the template text.


_.templateSettings.imports

#

(Object): Used to import variables into the compiled template.