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lodash-fp-documentation.md

lodash v4.17.20

Array

• _.chunk
• _.compact
• _.concat
• _.difference
• _.differenceBy
• _.differenceWith
• _.drop
• _.dropRight
• _.dropRightWhile
• _.dropWhile
• _.fill
• _.findIndex
• _.findLastIndex
• _.first -> head
• _.flatten
• _.flattenDeep
• _.flattenDepth
• _.fromPairs
• _.head
• _.indexOf
• _.initial
• _.intersection
• _.intersectionBy
• _.intersectionWith
• _.join
• _.last
• _.lastIndexOf
• _.nth
• _.pull
• _.pullAll
• _.pullAllBy
• _.pullAllWith
• _.pullAt
• _.remove
• _.reverse
• _.slice
• _.sortedIndex
• _.sortedIndexBy
• _.sortedIndexOf
• _.sortedLastIndex
• _.sortedLastIndexBy
• _.sortedLastIndexOf
• _.sortedUniq
• _.sortedUniqBy
• _.tail
• _.take
• _.takeRight
• _.takeRightWhile
• _.takeWhile
• _.union
• _.unionBy
• _.unionWith
• _.uniq
• _.uniqBy
• _.uniqWith
• _.unzip
• _.unzipWith
• _.without
• _.xor
• _.xorBy
• _.xorWith
• _.zip
• _.zipObject
• _.zipObjectDeep
• _.zipWith

Collection

• _.countBy
• _.each -> forEach
• _.eachRight -> forEachRight
• _.every
• _.filter
• _.find
• _.findLast
• _.flatMap
• _.flatMapDeep
• _.flatMapDepth
• _.forEach
• _.forEachRight
• _.groupBy
• _.includes
• _.invokeMap
• _.keyBy
• _.map
• _.orderBy
• _.partition
• _.reduce
• _.reduceRight
• _.reject
• _.sample
• _.sampleSize
• _.shuffle
• _.size
• _.some
• _.sortBy

Date

• _.now

Function

• _.after
• _.ary
• _.before
• _.bind
• _.bindKey
• _.curry
• _.curryRight
• _.debounce
• _.defer
• _.delay
• _.flip
• _.memoize
• _.negate
• _.once
• _.overArgs
• _.partial
• _.partialRight
• _.rearg
• _.rest
• _.spread
• _.throttle
• _.unary
• _.wrap

Lang

• _.castArray
• _.clone
• _.cloneDeep
• _.cloneDeepWith
• _.cloneWith
• _.conformsTo
• _.eq
• _.gt
• _.gte
• _.isArguments
• _.isArray
• _.isArrayBuffer
• _.isArrayLike
• _.isArrayLikeObject
• _.isBoolean
• _.isBuffer
• _.isDate
• _.isElement
• _.isEmpty
• _.isEqual
• _.isEqualWith
• _.isError
• _.isFinite
• _.isFunction
• _.isInteger
• _.isLength
• _.isMap
• _.isMatch
• _.isMatchWith
• _.isNaN
• _.isNative
• _.isNil
• _.isNull
• _.isNumber
• _.isObject
• _.isObjectLike
• _.isPlainObject
• _.isRegExp
• _.isSafeInteger
• _.isSet
• _.isString
• _.isSymbol
• _.isTypedArray
• _.isUndefined
• _.isWeakMap
• _.isWeakSet
• _.lt
• _.lte
• _.toArray
• _.toFinite
• _.toInteger
• _.toLength
• _.toNumber
• _.toPlainObject
• _.toSafeInteger
• _.toString

Math

• _.add
• _.ceil
• _.divide
• _.floor
• _.max
• _.maxBy
• _.mean
• _.meanBy
• _.min
• _.minBy
• _.multiply
• _.round
• _.subtract
• _.sum
• _.sumBy

Number

• _.clamp
• _.inRange
• _.random

Object

• _.assign
• _.assignIn
• _.assignInWith
• _.assignWith
• _.at
• _.create
• _.defaults
• _.defaultsDeep
• _.entries -> toPairs
• _.entriesIn -> toPairsIn
• _.extend -> assignIn
• _.extendWith -> assignInWith
• _.findKey
• _.findLastKey
• _.forIn
• _.forInRight
• _.forOwn
• _.forOwnRight
• _.functions
• _.functionsIn
• _.get
• _.has
• _.hasIn
• _.invert
• _.invertBy
• _.invoke
• _.keys
• _.keysIn
• _.mapKeys
• _.mapValues
• _.merge
• _.mergeWith
• _.omit
• _.omitBy
• _.pick
• _.pickBy
• _.result
• _.set
• _.setWith
• _.toPairs
• _.toPairsIn
• _.transform
• _.unset
• _.update
• _.updateWith
• _.values
• _.valuesIn

Seq

• _
• _.chain
• _.tap
• _.thru
• _.prototype[Symbol.iterator]
• _.prototype.at
• _.prototype.chain
• _.prototype.commit
• _.prototype.next
• _.prototype.plant
• _.prototype.reverse
• _.prototype.toJSON -> value
• _.prototype.value
• _.prototype.valueOf -> value

String

• _.camelCase
• _.capitalize
• _.deburr
• _.endsWith
• _.escape
• _.escapeRegExp
• _.kebabCase
• _.lowerCase
• _.lowerFirst
• _.pad
• _.padEnd
• _.padStart
• _.parseInt
• _.repeat
• _.replace
• _.snakeCase
• _.split
• _.startCase
• _.startsWith
• _.template
• _.toLower
• _.toUpper
• _.trim
• _.trimEnd
• _.trimStart
• _.truncate
• _.unescape
• _.upperCase
• _.upperFirst
• _.words

Util

• _.attempt
• _.bindAll
• _.cond
• _.conforms
• _.constant
• _.defaultTo
• _.flow
• _.flowRight
• _.identity
• _.iteratee
• _.matches
• _.matchesProperty
• _.method
• _.methodOf
• _.mixin
• _.noConflict
• _.noop
• _.nthArg
• _.over
• _.overEvery
• _.overSome
• _.property
• _.propertyOf
• _.range
• _.rangeRight
• _.runInContext
• _.stubArray
• _.stubFalse
• _.stubObject
• _.stubString
• _.stubTrue
• _.times
• _.toPath
• _.uniqueId

Properties

• _.VERSION
• _.templateSettings
• _.templateSettings.escape
• _.templateSettings.evaluate
• _.templateSettings.imports
• _.templateSettings.interpolate
• _.templateSettings.variable

Methods

• _.templateSettings.imports._

“Array” Methods

_.chunk(size, array)

# Ⓢ Ⓣ Ⓝ

Creates an array of elements split into groups the length of size. If array can't be split evenly, the final chunk will be the remaining elements.

Since

3.0.0

Arguments

1. size (number): The length of each chunk
2. array (Array): The array to process.

Returns

(Array): Returns the new array of chunks.

Example

_.chunk(2, ['a', 'b', 'c', 'd']);
// => [['a', 'b'], ['c', 'd']]

_.chunk(3, ['a', 'b', 'c', 'd']);
// => [['a', 'b', 'c'], ['d']]

---

_.compact(array)

# Ⓢ Ⓣ Ⓝ

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

Since

0.1.0

Arguments

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

Returns

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

Example

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

---

_.concat(array, values)

# Ⓢ Ⓣ Ⓝ

Creates a new array concatenating array with any additional arrays and/or values.

Since

4.0.0

Arguments

1. array (Array): The array to concatenate.
2. values (*|*[]): The values to concatenate.

Returns

(Array): Returns the new concatenated array.

Example

var array = [1];
var other = _.concat(array, [2, [3], [[4]]]);

// => [1, 2, 3, [4]]

// => [1]

---

_.difference(array, values)

# Ⓢ Ⓣ Ⓝ

Creates an array of array values not included in the other given arrays using SameValueZero for equality comparisons. The order and references of result values are determined by the first array.

Note: Unlike _.pullAll, this method returns a new array.

Since

0.1.0

Arguments

1. array (Array): The array to inspect.
2. values (Array|Array[]): The values to exclude.

Returns

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

Example

_.difference([2, 1], [2, 3]);
// => [1]

---

_.differenceBy(iteratee, array, values)

# Ⓢ Ⓣ Ⓝ

This method is like _.difference except that it accepts iteratee which is invoked for each element of array and values to generate the criterion by which they're compared. The order and references of result values are determined by the first array. The iteratee is invoked with one argument:
(value).

Note: Unlike _.pullAllBy, this method returns a new array.

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. array (Array): The array to inspect.
3. values (Array|Array[]): The values to exclude.

Returns

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

Example

_.differenceBy(Math.floor, [2.1, 1.2], [2.3, 3.4]);
// => [1.2]

// The `_.property` iteratee shorthand.
_.differenceBy('x', [{ 'x': 2 }, { 'x': 1 }], [{ 'x': 1 }]);
// => [{ 'x': 2 }]

---

_.differenceWith(comparator, array, values)

# Ⓢ Ⓣ Ⓝ

This method is like _.difference except that it accepts comparator which is invoked to compare elements of array to values. The order and references of result values are determined by the first array. The comparator is invoked with two arguments: (arrVal, othVal).

Note: Unlike _.pullAllWith, this method returns a new array.

Since

4.0.0

Arguments

1. comparator (Function): The comparator invoked per element.
2. array (Array): The array to inspect.
3. values (Array|Array[]): The values to exclude.

Returns

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

Example

var objects = [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }];

_.differenceWith(_.isEqual, objects, [{ 'x': 1, 'y': 2 }]);
// => [{ 'x': 2, 'y': 1 }]

---

_.drop(n, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array with n elements dropped from the beginning.

Since

0.5.0

Arguments

1. n (number): The number of elements to drop.
2. array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Example

_.drop(1, [1, 2, 3]);
// => [2, 3]

_.drop(2, [1, 2, 3]);
// => [3]

_.drop(5, [1, 2, 3]);
// => []

_.drop(0, [1, 2, 3]);
// => [1, 2, 3]

---

_.dropRight(n, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array with n elements dropped from the end.

Since

3.0.0

Arguments

1. n (number): The number of elements to drop.
2. array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Example

_.dropRight(1, [1, 2, 3]);
// => [1, 2]

_.dropRight(2, [1, 2, 3]);
// => [1]

_.dropRight(5, [1, 2, 3]);
// => []

_.dropRight(0, [1, 2, 3]);
// => [1, 2, 3]

---

_.dropRightWhile(predicate, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array excluding elements dropped from the end. Elements are dropped until predicate returns falsey. The predicate is invoked with three arguments: (value, index, array).

Since

3.0.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Example

var users = [
  { 'user': 'barney',  'active': true },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': false }
];

_.dropRightWhile(function(o) { return !o.active; }, users);
// => objects for ['barney']

// The `_.matches` iteratee shorthand.
_.dropRightWhile({ 'user': 'pebbles', 'active': false }, users);
// => objects for ['barney', 'fred']

// The `_.matchesProperty` iteratee shorthand.
_.dropRightWhile(['active', false], users);
// => objects for ['barney']

// The `_.property` iteratee shorthand.
_.dropRightWhile('active', users);
// => objects for ['barney', 'fred', 'pebbles']

---

_.dropWhile(predicate, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array excluding elements dropped from the beginning. Elements are dropped until predicate returns falsey. The predicate is invoked with three arguments: (value, index, array).

Since

3.0.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Example

var users = [
  { 'user': 'barney',  'active': false },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': true }
];

_.dropWhile(function(o) { return !o.active; }, users);
// => objects for ['pebbles']

// The `_.matches` iteratee shorthand.
_.dropWhile({ 'user': 'barney', 'active': false }, users);
// => objects for ['fred', 'pebbles']

// The `_.matchesProperty` iteratee shorthand.
_.dropWhile(['active', false], users);
// => objects for ['pebbles']

// The `_.property` iteratee shorthand.
_.dropWhile('active', users);
// => objects for ['barney', 'fred', 'pebbles']

---

_.fill(start, end, value, array)

# Ⓢ Ⓣ Ⓝ

Fills elements of array with value from start up to, but not including, end.

Since

3.2.0

Arguments

1. start (number): The start position.
2. end (number): The end position.
3. value (*): The value to fill array with.
4. array (Array): The array to fill.

Returns

(Array): Returns array.

Example

var array = [1, 2, 3];

_.fill(0, array.length, 'a', array);
// => ['a', 'a', 'a']

_.fill(0, Array(3).length, 2, Array(3));
// => [2, 2, 2]

_.fill(1, 3, '*', [4, 6, 8, 10]);
// => [4, '*', '*', 10]

---

_.findIndex(predicate, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.find except that it returns the index of the first element predicate returns truthy for instead of the element itself.

Since

1.1.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. array (Array): The array to inspect.

Returns

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

Example

var users = [
  { 'user': 'barney',  'active': false },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': true }
];

_.findIndex(function(o) { return o.user == 'barney'; }, users);
// => 0

// The `_.matches` iteratee shorthand.
_.findIndex({ 'user': 'fred', 'active': false }, users);
// => 1

// The `_.matchesProperty` iteratee shorthand.
_.findIndex(['active', false], users);
// => 0

// The `_.property` iteratee shorthand.
_.findIndex('active', users);
// => 2

---

_.findLastIndex(predicate, array)

# Ⓢ Ⓣ Ⓝ

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

Since

2.0.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. array (Array): The array to inspect.

Returns

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

Example

var users = [
  { 'user': 'barney',  'active': true },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': false }
];

_.findLastIndex(function(o) { return o.user == 'pebbles'; }, users);
// => 2

// The `_.matches` iteratee shorthand.
_.findLastIndex({ 'user': 'barney', 'active': true }, users);
// => 0

// The `_.matchesProperty` iteratee shorthand.
_.findLastIndex(['active', false], users);
// => 2

// The `_.property` iteratee shorthand.
_.findLastIndex('active', users);
// => 0

---

_.flatten(array)

# Ⓢ Ⓣ Ⓝ

Flattens array a single level deep.

Since

0.1.0

Arguments

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

Returns

(Array): Returns the new flattened array.

Example

_.flatten([1, [2, [3, [4]], 5]]);
// => [1, 2, [3, [4]], 5]

---

_.flattenDeep(array)

# Ⓢ Ⓣ Ⓝ

Recursively flattens array.

Since

3.0.0

Arguments

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

Returns

(Array): Returns the new flattened array.

Example

_.flattenDeep([1, [2, [3, [4]], 5]]);
// => [1, 2, 3, 4, 5]

---

_.flattenDepth(depth, array)

# Ⓢ Ⓣ Ⓝ

Recursively flatten array up to depth times.

Since

4.4.0

Arguments

1. depth (number): The maximum recursion depth.
2. array (Array): The array to flatten.

Returns

(Array): Returns the new flattened array.

Example

var array = [1, [2, [3, [4]], 5]];

_.flattenDepth(1, array);
// => [1, 2, [3, [4]], 5]

_.flattenDepth(2, array);
// => [1, 2, 3, [4], 5]

---

_.fromPairs(pairs)

# Ⓢ Ⓣ Ⓝ

The inverse of _.toPairs; this method returns an object composed from key-value pairs.

Since

4.0.0

Arguments

1. pairs (Array): The key-value pairs.

Returns

(Object): Returns the new object.

Example

_.fromPairs([['a', 1], ['b', 2]]);
// => { 'a': 1, 'b': 2 }

---

_.head(array)

# Ⓢ Ⓣ Ⓝ

Gets the first element of array.

Since

0.1.0

Aliases

_.first

Arguments

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

Returns

(*): Returns the first element of array.

Example

_.head([1, 2, 3]);
// => 1

_.head([]);
// => undefined

---

_.indexOf(value, array)

# Ⓢ Ⓣ Ⓝ

Gets the index at which the first occurrence of value is found in array using SameValueZero for equality comparisons. If fromIndex is negative, it's used as the offset from the end of array.

Since

0.1.0

Arguments

1. value (*): The value to search for.
2. array (Array): The array to inspect.

Returns

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

Example

_.indexOf(2, [1, 2, 1, 2]);
// => 1

// Search from the `fromIndex`.
_.indexOf([2, 2], [1, 2, 1, 2]);
// => 3

---

_.initial(array)

# Ⓢ Ⓣ Ⓝ

Gets all but the last element of array.

Since

0.1.0

Arguments

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

Returns

(Array): Returns the slice of array.

Example

_.initial([1, 2, 3]);
// => [1, 2]

---

_.intersection(arrays, arrays)

# Ⓢ Ⓣ Ⓝ

Creates an array of unique values that are included in all given arrays using SameValueZero for equality comparisons. The order and references of result values are determined by the first array.

Since

0.1.0

Arguments

1. arrays (Array): The arrays to inspect.
2. arrays (Array): The arrays to inspect.

Returns

(Array): Returns the new array of intersecting values.

Example

_.intersection([2, 3], [2, 1]);
// => [2]

---

_.intersectionBy(iteratee, arrays, arrays)

# Ⓢ Ⓣ Ⓝ

This method is like _.intersection except that it accepts iteratee which is invoked for each element of each arrays to generate the criterion by which they're compared. The order and references of result values are determined by the first array. The iteratee is invoked with one argument:
(value).

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. arrays (Array): The arrays to inspect.
3. arrays (Array): The arrays to inspect.

Returns

(Array): Returns the new array of intersecting values.

Example

_.intersectionBy(Math.floor, [2.1, 1.2], [2.3, 3.4]);
// => [2.1]

// The `_.property` iteratee shorthand.
_.intersectionBy('x', [{ 'x': 1 }], [{ 'x': 2 }, { 'x': 1 }]);
// => [{ 'x': 1 }]

---

_.intersectionWith(comparator, arrays, arrays)

# Ⓢ Ⓣ Ⓝ

This method is like _.intersection except that it accepts comparator which is invoked to compare elements of arrays. The order and references of result values are determined by the first array. The comparator is invoked with two arguments: (arrVal, othVal).

Since

4.0.0

Arguments

1. comparator (Function): The comparator invoked per element.
2. arrays (Array): The arrays to inspect.
3. arrays (Array): The arrays to inspect.

Returns

(Array): Returns the new array of intersecting values.

Example

var objects = [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }];
var others = [{ 'x': 1, 'y': 1 }, { 'x': 1, 'y': 2 }];

_.intersectionWith(_.isEqual, objects, others);
// => [{ 'x': 1, 'y': 2 }]

---

_.join(separator, array)

# Ⓢ Ⓣ Ⓝ

Converts all elements in array into a string separated by separator.

Since

4.0.0

Arguments

1. separator (string): The element separator.
2. array (Array): The array to convert.

Returns

(string): Returns the joined string.

Example

_.join('~', ['a', 'b', 'c']);
// => 'a~b~c'

---

_.last(array)

# Ⓢ Ⓣ Ⓝ

Gets the last element of array.

Since

0.1.0

Arguments

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

Returns

(*): Returns the last element of array.

Example

_.last([1, 2, 3]);
// => 3

---

_.lastIndexOf(value, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.indexOf except that it iterates over elements of array from right to left.

Since

0.1.0

Arguments

1. value (*): The value to search for.
2. array (Array): The array to inspect.

Returns

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

Example

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

// Search from the `fromIndex`.
_.lastIndexOf([2, 2], [1, 2, 1, 2]);
// => 1

---

_.nth(n, array)

# Ⓢ Ⓣ Ⓝ

Gets the element at index n of array. If n is negative, the nth element from the end is returned.

Since

4.11.0

Arguments

1. n (number): The index of the element to return.
2. array (Array): The array to query.

Returns

(*): Returns the nth element of array.

Example

var array = ['a', 'b', 'c', 'd'];

_.nth(1, array);
// => 'b'

_.nth(-2, array);
// => 'c';

---

_.pull(values, array)

# Ⓢ Ⓣ Ⓝ

Removes all given values from array using SameValueZero for equality comparisons.

Since

2.0.0

Arguments

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

Returns

(Array): Returns array.

Example

var array = ['a', 'b', 'c', 'a', 'b', 'c'];

_.pull(['a', 'c'], array);
// => ['b', 'b']

---

_.pullAll(values, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.pull except that it accepts an array of values to remove.

Since

4.0.0

Arguments

1. values (Array): The values to remove.
2. array (Array): The array to modify.

Returns

(Array): Returns array.

Example

var array = ['a', 'b', 'c', 'a', 'b', 'c'];

_.pullAll(['a', 'c'], array);
// => ['b', 'b']

---

_.pullAllBy(iteratee, values, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.pullAll except that it accepts iteratee which is invoked for each element of array and values to generate the criterion by which they're compared. The iteratee is invoked with one argument: (value).

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. values (Array): The values to remove.
3. array (Array): The array to modify.

Returns

(Array): Returns array.

Example

var array = [{ 'x': 1 }, { 'x': 2 }, { 'x': 3 }, { 'x': 1 }];

_.pullAllBy('x', [{ 'x': 1 }, { 'x': 3 }], array);
// => [{ 'x': 2 }]

---

_.pullAllWith(comparator, values, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.pullAll except that it accepts comparator which is invoked to compare elements of array to values. The comparator is invoked with two arguments: (arrVal, othVal).

Since

4.6.0

Arguments

1. comparator (Function): The comparator invoked per element.
2. values (Array): The values to remove.
3. array (Array): The array to modify.

Returns

(Array): Returns array.

Example

var array = [{ 'x': 1, 'y': 2 }, { 'x': 3, 'y': 4 }, { 'x': 5, 'y': 6 }];

_.pullAllWith(_.isEqual, [{ 'x': 3, 'y': 4 }], array);
// => [{ 'x': 1, 'y': 2 }, { 'x': 5, 'y': 6 }]

---

_.pullAt(indexes, array)

# Ⓢ Ⓣ Ⓝ

Removes elements from array corresponding to indexes and returns an array of removed elements.

Since

3.0.0

Arguments

1. indexes (number|number[]): The indexes of elements to remove.
2. array (Array): The array to modify.

Returns

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

Example

var array = ['a', 'b', 'c', 'd'];
var pulled = _.pullAt([1, 3], array);

// => ['a', 'c']

// => ['b', 'd']

---

_.remove(predicate, array)

# Ⓢ Ⓣ Ⓝ

Removes all elements from array that predicate returns truthy for and returns an array of the removed elements. The predicate is invoked with three arguments: (value, index, array).

Since

2.0.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. array (Array): The array to modify.

Returns

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

Example

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

// => [1, 3]

// => [2, 4]

---

_.reverse(array)

# Ⓢ Ⓣ Ⓝ

Reverses array so that the first element becomes the last, the second element becomes the second to last, and so on.

Since

4.0.0

Arguments

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

Returns

(Array): Returns array.

Example

var array = [1, 2, 3];

_.reverse(array);
// => [3, 2, 1]

// => [3, 2, 1]

---

_.slice(start, end, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array from start up to, but not including, end.

Note: This method is used instead of Array#slice to ensure dense arrays are returned.

Since

3.0.0

Arguments

1. start (number): The start position.
2. end (number): The end position.
3. array (Array): The array to slice.

Returns

(Array): Returns the slice of array.

---

_.sortedIndex(value, array)

# Ⓢ Ⓣ Ⓝ

Uses a binary search to determine the lowest index at which value should be inserted into array in order to maintain its sort order.

Since

0.1.0

Arguments

1. value (*): The value to evaluate.
2. array (Array): The sorted array to inspect.

Returns

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

Example

_.sortedIndex(40, [30, 50]);
// => 1

---

_.sortedIndexBy(iteratee, value, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.sortedIndex except that it accepts iteratee which is invoked for value and each element of array to compute their sort ranking. The iteratee is invoked with one argument: (value).

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. value (*): The value to evaluate.
3. array (Array): The sorted array to inspect.

Returns

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

Example

var objects = [{ 'x': 4 }, { 'x': 5 }];

_.sortedIndexBy(function(o) { return o.x; }, { 'x': 4 }, objects);
// => 0

// The `_.property` iteratee shorthand.
_.sortedIndexBy('x', { 'x': 4 }, objects);
// => 0

---

_.sortedIndexOf(value, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.indexOf except that it performs a binary search on a sorted array.

Since

4.0.0

Arguments

1. value (*): The value to search for.
2. array (Array): The array to inspect.

Returns

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

Example

_.sortedIndexOf(5, [4, 5, 5, 5, 6]);
// => 1

---

_.sortedLastIndex(value, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.sortedIndex except that it returns the highest index at which value should be inserted into array in order to maintain its sort order.

Since

3.0.0

Arguments

1. value (*): The value to evaluate.
2. array (Array): The sorted array to inspect.

Returns

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

Example

_.sortedLastIndex(5, [4, 5, 5, 5, 6]);
// => 4

---

_.sortedLastIndexBy(iteratee, value, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.sortedLastIndex except that it accepts iteratee which is invoked for value and each element of array to compute their sort ranking. The iteratee is invoked with one argument: (value).

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. value (*): The value to evaluate.
3. array (Array): The sorted array to inspect.

Returns

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

Example

var objects = [{ 'x': 4 }, { 'x': 5 }];

_.sortedLastIndexBy(function(o) { return o.x; }, { 'x': 4 }, objects);
// => 1

// The `_.property` iteratee shorthand.
_.sortedLastIndexBy('x', { 'x': 4 }, objects);
// => 1

---

_.sortedLastIndexOf(value, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.lastIndexOf except that it performs a binary search on a sorted array.

Since

4.0.0

Arguments

1. value (*): The value to search for.
2. array (Array): The array to inspect.

Returns

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

Example

_.sortedLastIndexOf(5, [4, 5, 5, 5, 6]);
// => 3

---

_.sortedUniq(array)

# Ⓢ Ⓣ Ⓝ

This method is like _.uniq except that it's designed and optimized for sorted arrays.

Since

4.0.0

Arguments

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

Returns

(Array): Returns the new duplicate free array.

Example

_.sortedUniq([1, 1, 2]);
// => [1, 2]

---

_.sortedUniqBy(iteratee, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.uniqBy except that it's designed and optimized for sorted arrays.

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. array (Array): The array to inspect.

Returns

(Array): Returns the new duplicate free array.

Example

_.sortedUniqBy(Math.floor, [1.1, 1.2, 2.3, 2.4]);
// => [1.1, 2.3]

---

_.tail(array)

# Ⓢ Ⓣ Ⓝ

Gets all but the first element of array.

Since

4.0.0

Arguments

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

Returns

(Array): Returns the slice of array.

Example

_.tail([1, 2, 3]);
// => [2, 3]

---

_.take(n, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array with n elements taken from the beginning.

Since

0.1.0

Arguments

1. n (number): The number of elements to take.
2. array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Example

_.take(1, [1, 2, 3]);
// => [1]

_.take(2, [1, 2, 3]);
// => [1, 2]

_.take(5, [1, 2, 3]);
// => [1, 2, 3]

_.take(0, [1, 2, 3]);
// => []

---

_.takeRight(n, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array with n elements taken from the end.

Since

3.0.0

Arguments

1. n (number): The number of elements to take.
2. array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Example

_.takeRight(1, [1, 2, 3]);
// => [3]

_.takeRight(2, [1, 2, 3]);
// => [2, 3]

_.takeRight(5, [1, 2, 3]);
// => [1, 2, 3]

_.takeRight(0, [1, 2, 3]);
// => []

---

_.takeRightWhile(predicate, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array with elements taken from the end. Elements are taken until predicate returns falsey. The predicate is invoked with three arguments: (value, index, array).

Since

3.0.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Example

var users = [
  { 'user': 'barney',  'active': true },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': false }
];

_.takeRightWhile(function(o) { return !o.active; }, users);
// => objects for ['fred', 'pebbles']

// The `_.matches` iteratee shorthand.
_.takeRightWhile({ 'user': 'pebbles', 'active': false }, users);
// => objects for ['pebbles']

// The `_.matchesProperty` iteratee shorthand.
_.takeRightWhile(['active', false], users);
// => objects for ['fred', 'pebbles']

// The `_.property` iteratee shorthand.
_.takeRightWhile('active', users);
// => []

---

_.takeWhile(predicate, array)

# Ⓢ Ⓣ Ⓝ

Creates a slice of array with elements taken from the beginning. Elements are taken until predicate returns falsey. The predicate is invoked with three arguments: (value, index, array).

Since

3.0.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Example

var users = [
  { 'user': 'barney',  'active': false },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': true }
];

_.takeWhile(function(o) { return !o.active; }, users);
// => objects for ['barney', 'fred']

// The `_.matches` iteratee shorthand.
_.takeWhile({ 'user': 'barney', 'active': false }, users);
// => objects for ['barney']

// The `_.matchesProperty` iteratee shorthand.
_.takeWhile(['active', false], users);
// => objects for ['barney', 'fred']

// The `_.property` iteratee shorthand.
_.takeWhile('active', users);
// => []

---

_.union(arrays, arrays)

# Ⓢ Ⓣ Ⓝ

Creates an array of unique values, in order, from all given arrays using SameValueZero for equality comparisons.

Since

0.1.0

Arguments

1. arrays (Array): The arrays to inspect.
2. arrays (Array): The arrays to inspect.

Returns

(Array): Returns the new array of combined values.

Example

_.union([1, 2], [2]);
// => [2, 1]

---

_.unionBy(iteratee, arrays, arrays)

# Ⓢ Ⓣ Ⓝ

This method is like _.union except that it accepts iteratee which is invoked for each element of each arrays to generate the criterion by which uniqueness is computed. Result values are chosen from the first array in which the value occurs. The iteratee is invoked with one argument:
(value).

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. arrays (Array): The arrays to inspect.
3. arrays (Array): The arrays to inspect.

Returns

(Array): Returns the new array of combined values.

Example

_.unionBy(Math.floor, [2.1], [1.2, 2.3]);
// => [2.1, 1.2]

// The `_.property` iteratee shorthand.
_.unionBy('x', [{ 'x': 1 }], [{ 'x': 2 }, { 'x': 1 }]);
// => [{ 'x': 1 }, { 'x': 2 }]

---

_.unionWith(comparator, arrays, arrays)

# Ⓢ Ⓣ Ⓝ

This method is like _.union except that it accepts comparator which is invoked to compare elements of arrays. Result values are chosen from the first array in which the value occurs. The comparator is invoked with two arguments: (arrVal, othVal).

Since

4.0.0

Arguments

1. comparator (Function): The comparator invoked per element.
2. arrays (Array): The arrays to inspect.
3. arrays (Array): The arrays to inspect.

Returns

(Array): Returns the new array of combined values.

Example

var objects = [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }];
var others = [{ 'x': 1, 'y': 1 }, { 'x': 1, 'y': 2 }];

_.unionWith(_.isEqual, objects, others);
// => [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }, { 'x': 1, 'y': 1 }]

---

_.uniq(array)

# Ⓢ Ⓣ Ⓝ

Creates a duplicate-free version of an array, using SameValueZero for equality comparisons, in which only the first occurrence of each element is kept. The order of result values is determined by the order they occur in the array.

Since

0.1.0

Arguments

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

Returns

(Array): Returns the new duplicate free array.

Example

_.uniq([2, 1, 2]);
// => [2, 1]

---

_.uniqBy(iteratee, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.uniq except that it accepts iteratee which is invoked for each element in array to generate the criterion by which uniqueness is computed. The order of result values is determined by the order they occur in the array. The iteratee is invoked with one argument:
(value).

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. array (Array): The array to inspect.

Returns

(Array): Returns the new duplicate free array.

Example

_.uniqBy(Math.floor, [2.1, 1.2, 2.3]);
// => [2.1, 1.2]

// The `_.property` iteratee shorthand.
_.uniqBy('x', [{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }]);
// => [{ 'x': 1 }, { 'x': 2 }]

---

_.uniqWith(comparator, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.uniq except that it accepts comparator which is invoked to compare elements of array. The order of result values is determined by the order they occur in the array.The comparator is invoked with two arguments: (arrVal, othVal).

Since

4.0.0

Arguments

1. comparator (Function): The comparator invoked per element.
2. array (Array): The array to inspect.

Returns

(Array): Returns the new duplicate free array.

Example

var objects = [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }, { 'x': 1, 'y': 2 }];

_.uniqWith(_.isEqual, objects);
// => [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }]

---

_.unzip(array)

# Ⓢ Ⓣ Ⓝ

This method is like _.zip except that it accepts an array of grouped elements and creates an array regrouping the elements to their pre-zip configuration.

Since

1.2.0

Arguments

1. array (Array): The array of grouped elements to process.

Returns

(Array): Returns the new array of regrouped elements.

Example

var zipped = _.zip(['a', 'b'], [[1, 2], [true, false]]);
// => [['a', 1, true], ['b', 2, false]]

_.unzip(zipped);
// => [['a', 'b'], [1, 2], [true, false]]

---

_.unzipWith(iteratee, array)

# Ⓢ Ⓣ Ⓝ

This method is like _.unzip except that it accepts iteratee to specify how regrouped values should be combined. The iteratee is invoked with the elements of each group: (...group).

Since

3.8.0

Arguments

1. iteratee (Function): The function to combine regrouped values.
2. array (Array): The array of grouped elements to process.

Returns

(Array): Returns the new array of regrouped elements.

Example

var zipped = _.zip([1, 2], [[10, 20], [100, 200]]);
// => [[1, 10, 100], [2, 20, 200]]

_.unzipWith(_.add, zipped);
// => [3, 30, 300]

---

_.without(values, array)

# Ⓢ Ⓣ Ⓝ

Creates an array excluding all given values using SameValueZero for equality comparisons.

Note: Unlike _.pull, this method returns a new array.

Since

0.1.0

Arguments

1. values (*|*[]): The values to exclude.
2. array (Array): The array to inspect.

Returns

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

Example

_.without([1, 2], [2, 1, 2, 3]);
// => [3]

---

_.xor(arrays, arrays)

# Ⓢ Ⓣ Ⓝ

Creates an array of unique values that is the symmetric difference of the given arrays. The order of result values is determined by the order they occur in the arrays.

Since

2.4.0

Arguments

1. arrays (Array): The arrays to inspect.
2. arrays (Array): The arrays to inspect.

Returns

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

Example

_.xor([2, 3], [2, 1]);
// => [1, 3]

---

_.xorBy(iteratee, arrays, arrays)

# Ⓢ Ⓣ Ⓝ

This method is like _.xor except that it accepts iteratee which is invoked for each element of each arrays to generate the criterion by which by which they're compared. The order of result values is determined by the order they occur in the arrays. The iteratee is invoked with one argument: (value).

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee invoked per element.
2. arrays (Array): The arrays to inspect.
3. arrays (Array): The arrays to inspect.

Returns

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

Example

_.xorBy(Math.floor, [2.1, 1.2], [2.3, 3.4]);
// => [1.2, 3.4]

// The `_.property` iteratee shorthand.
_.xorBy('x', [{ 'x': 1 }], [{ 'x': 2 }, { 'x': 1 }]);
// => [{ 'x': 2 }]

---

_.xorWith(comparator, arrays, arrays)

# Ⓢ Ⓣ Ⓝ

This method is like _.xor except that it accepts comparator which is invoked to compare elements of arrays. The order of result values is determined by the order they occur in the arrays. The comparator is invoked with two arguments: (arrVal, othVal).

Since

4.0.0

Arguments

1. comparator (Function): The comparator invoked per element.
2. arrays (Array): The arrays to inspect.
3. arrays (Array): The arrays to inspect.

Returns

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

Example

var objects = [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }];
var others = [{ 'x': 1, 'y': 1 }, { 'x': 1, 'y': 2 }];

_.xorWith(_.isEqual, objects, others);
// => [{ 'x': 2, 'y': 1 }, { 'x': 1, 'y': 1 }]

---

_.zip(arrays, arrays)

# Ⓢ Ⓣ Ⓝ

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.

Since

0.1.0

Arguments

1. arrays (Array): The arrays to process.
2. arrays (Array): The arrays to process.

Returns

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

Example

_.zip(['a', 'b'], [[1, 2], [true, false]]);
// => [['a', 1, true], ['b', 2, false]]

---

_.zipObject(props, values)

# Ⓢ Ⓣ Ⓝ

This method is like _.fromPairs except that it accepts two arrays, one of property identifiers and one of corresponding values.

Since

0.4.0

Arguments

1. props (Array): The property identifiers.
2. values (Array): The property values.

Returns

(Object): Returns the new object.

Example

_.zipObject(['a', 'b'], [1, 2]);
// => { 'a': 1, 'b': 2 }

---

_.zipObjectDeep(props, values)

# Ⓢ Ⓣ Ⓝ

This method is like _.zipObject except that it supports property paths.

Since

4.1.0

Arguments

1. props (Array): The property identifiers.
2. values (Array): The property values.

Returns

(Object): Returns the new object.

Example

_.zipObjectDeep(['a.b[0].c', 'a.b[1].d'], [1, 2]);
// => { 'a': { 'b': [{ 'c': 1 }, { 'd': 2 }] } }

---

_.zipWith(iteratee, arrays, arrays)

# Ⓢ Ⓣ Ⓝ

This method is like _.zip except that it accepts iteratee to specify how grouped values should be combined. The iteratee is invoked with the elements of each group: (...group).

Since

3.8.0

Arguments

1. iteratee (Function): The function to combine grouped values.
2. arrays (Array): The arrays to process.
3. arrays (Array): The arrays to process.

Returns

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

Example

_.zipWith([[100, 200], function(a, b, c) {
  return a + b + c;
}], [1, 2], [10, 20]);
// => [111, 222]

---

“Collection” Methods

_.countBy(iteratee, collection)

# Ⓢ Ⓣ Ⓝ

Creates an object composed of keys generated from the results of running each element of collection thru iteratee. The corresponding value of each key is the number of times the key was returned by iteratee. The iteratee is invoked with one argument: (value).

Since

0.5.0

Arguments

1. iteratee (Function): The iteratee to transform keys.
2. collection (Array|Object): The collection to iterate over.

Returns

(Object): Returns the composed aggregate object.

Example

_.countBy(Math.floor, [6.1, 4.2, 6.3]);
// => { '4': 1, '6': 2 }

// The `_.property` iteratee shorthand.
_.countBy('length', ['one', 'two', 'three']);
// => { '3': 2, '5': 1 }

---

_.every(predicate, collection)

# Ⓢ Ⓣ Ⓝ

Checks if predicate returns truthy for all elements of collection. Iteration is stopped once predicate returns falsey. The predicate is invoked with three arguments: (value, index|key, collection).

Note: This method returns true for empty collections because everything is true of elements of empty collections.

Since

0.1.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(boolean): Returns true if all elements pass the predicate check, else false.

Example

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

var users = [
  { 'user': 'barney', 'age': 36, 'active': false },
  { 'user': 'fred',   'age': 40, 'active': false }
];

// The `_.matches` iteratee shorthand.
_.every({ 'user': 'barney', 'active': false }, users);
// => false

// The `_.matchesProperty` iteratee shorthand.
_.every(['active', false], users);
// => true

// The `_.property` iteratee shorthand.
_.every('active', users);
// => false

---

_.filter(predicate, collection)

# Ⓢ Ⓣ Ⓝ

Iterates over elements of collection, returning an array of all elements predicate returns truthy for. The predicate is invoked with three arguments: (value, index|key, collection).

Note: Unlike _.remove, this method returns a new array.

Since

0.1.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the new filtered array.

Example

var users = [
  { 'user': 'barney', 'age': 36, 'active': true },
  { 'user': 'fred',   'age': 40, 'active': false }
];

_.filter(function(o) { return !o.active; }, users);
// => objects for ['fred']

// The `_.matches` iteratee shorthand.
_.filter({ 'age': 36, 'active': true }, users);
// => objects for ['barney']

// The `_.matchesProperty` iteratee shorthand.
_.filter(['active', false], users);
// => objects for ['fred']

// The `_.property` iteratee shorthand.
_.filter('active', users);
// => objects for ['barney']

// Combining several predicates using `_.overEvery` or `_.overSome`.
_.filter(_.overSome([{ 'age': 36 }, ['age', 40]]), users);
// => objects for ['fred', 'barney']

---

_.find(predicate, collection)

# Ⓢ Ⓣ Ⓝ

Iterates over elements of collection, returning the first element predicate returns truthy for. The predicate is invoked with three arguments: (value, index|key, collection).

Since

0.1.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to inspect.

Returns

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

Example

var users = [
  { 'user': 'barney',  'age': 36, 'active': true },
  { 'user': 'fred',    'age': 40, 'active': false },
  { 'user': 'pebbles', 'age': 1,  'active': true }
];

_.find(function(o) { return o.age < 40; }, users);
// => object for 'barney'

// The `_.matches` iteratee shorthand.
_.find({ 'age': 1, 'active': true }, users);
// => object for 'pebbles'

// The `_.matchesProperty` iteratee shorthand.
_.find(['active', false], users);
// => object for 'fred'

// The `_.property` iteratee shorthand.
_.find('active', users);
// => object for 'barney'

---

_.findLast(predicate, collection)

# Ⓢ Ⓣ Ⓝ

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

Since

2.0.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to inspect.

Returns

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

Example

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

---

_.flatMap(iteratee, collection)

# Ⓢ Ⓣ Ⓝ

Creates a flattened array of values by running each element in collection thru iteratee and flattening the mapped results. The iteratee is invoked with three arguments: (value, index|key, collection).

Since

4.0.0

Arguments

1. iteratee (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the new flattened array.

Example

function duplicate(n) {
  return [n, n];
}

_.flatMap(duplicate, [1, 2]);
// => [1, 1, 2, 2]

---

_.flatMapDeep(iteratee, collection)

# Ⓢ Ⓣ Ⓝ

This method is like _.flatMap except that it recursively flattens the mapped results.

Since

4.7.0

Arguments

1. iteratee (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the new flattened array.

Example

function duplicate(n) {
  return [[[n, n]]];
}

_.flatMapDeep(duplicate, [1, 2]);
// => [1, 1, 2, 2]

---

_.flatMapDepth(iteratee, depth, collection)

# Ⓢ Ⓣ Ⓝ

This method is like _.flatMap except that it recursively flattens the mapped results up to depth times.

Since

4.7.0

Arguments

1. iteratee (Function): The function invoked per iteration.
2. depth (number): The maximum recursion depth.
3. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the new flattened array.

Example

function duplicate(n) {
  return [[[n, n]]];
}

_.flatMapDepth(duplicate, 2, [1, 2]);
// => [[1, 1], [2, 2]]

---

_.forEach(iteratee, collection)

# Ⓢ Ⓣ Ⓝ

Iterates over elements of collection and invokes iteratee for each element. The iteratee is invoked with three arguments: (value, index|key, collection). Iteratee functions 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 use _.forIn or _.forOwn for object iteration.

Since

0.1.0

Aliases

_.each

Arguments

1. iteratee (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(*): Returns collection.

Example

_.forEach(function(value) {
  console.log(value);
}, [1, 2]);
// => Logs `1` then `2`.

_.forEach(function(value, key) {
  console.log(key);
}, { 'a': 1, 'b': 2 });
// => Logs 'a' then 'b' (iteration order is not guaranteed).

---

_.forEachRight(iteratee, collection)

# Ⓢ Ⓣ Ⓝ

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

Since

2.0.0

Aliases

_.eachRight

Arguments

1. iteratee (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(*): Returns collection.

Example

_.forEachRight(function(value) {
  console.log(value);
}, [1, 2]);
// => Logs `2` then `1`.

---

_.groupBy(iteratee, collection)

# Ⓢ Ⓣ Ⓝ

Creates an object composed of keys generated from the results of running each element of collection thru iteratee. The order of grouped values is determined by the order they occur in collection. The corresponding value of each key is an array of elements responsible for generating the key. The iteratee is invoked with one argument: (value).

Since

0.1.0

Arguments

1. iteratee (Function): The iteratee to transform keys.
2. collection (Array|Object): The collection to iterate over.

Returns

(Object): Returns the composed aggregate object.

Example

_.groupBy(Math.floor, [6.1, 4.2, 6.3]);
// => { '4': [4.2], '6': [6.1, 6.3] }

// The `_.property` iteratee shorthand.
_.groupBy('length', ['one', 'two', 'three']);
// => { '3': ['one', 'two'], '5': ['three'] }

---

_.includes(value, collection)

# Ⓢ Ⓣ Ⓝ

Checks if value is in collection. If collection is a string, it's checked for a substring of value, otherwise SameValueZero is used for equality comparisons. If fromIndex is negative, it's used as the offset from the end of collection.

Since

0.1.0

Arguments

1. value (*): The value to search for.
2. collection (Array|Object|string): The collection to inspect.

Returns

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

Example

_.includes(1, [1, 2, 3]);
// => true

_.includes([1, 2], [1, 2, 3]);
// => false

_.includes(1, { 'a': 1, 'b': 2 });
// => true

_.includes('bc', 'abcd');
// => true

---

_.invokeMap(path, collection)

# Ⓢ Ⓣ Ⓝ

Invokes the method at path of each element in collection, returning an array of the results of each invoked method. Any additional arguments are provided to each invoked method. If path is a function, it's invoked for, and this bound to, each element in collection.

Since

4.0.0

Arguments

1. path (Array|Function|string): The path of the method to invoke or the function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the array of results.

Example

_.invokeMap('sort', [[5, 1, 7], [3, 2, 1]]);
// => [[1, 5, 7], [1, 2, 3]]

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

---

_.keyBy(iteratee, collection)

# Ⓢ Ⓣ Ⓝ

Creates an object composed of keys generated from the results of running each element of collection thru iteratee. The corresponding value of each key is the last element responsible for generating the key. The iteratee is invoked with one argument: (value).

Since

4.0.0

Arguments

1. iteratee (Function): The iteratee to transform keys.
2. collection (Array|Object): The collection to iterate over.

Returns

(Object): Returns the composed aggregate object.

Example

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

_.keyBy(function(o) {
  return String.fromCharCode(o.code);
}, array);
// => { 'a': { 'dir': 'left', 'code': 97 }, 'd': { 'dir': 'right', 'code': 100 } }

_.keyBy('dir', array);
// => { 'left': { 'dir': 'left', 'code': 97 }, 'right': { 'dir': 'right', 'code': 100 } }

---

_.map(iteratee, collection)

# Ⓢ Ⓣ Ⓝ

Creates an array of values by running each element in collection thru iteratee. The iteratee is invoked with three arguments:
(value, index|key, collection).

Many lodash methods are guarded to work as iteratees for methods like _.every, _.filter, _.map, _.mapValues, _.reject, and _.some.

The guarded methods are:
ary, chunk, curry, curryRight, drop, dropRight, every, fill, invert, parseInt, random, range, rangeRight, repeat, sampleSize, slice, some, sortBy, split, take, takeRight, template, trim, trimEnd, trimStart, and words

Since

0.1.0

Arguments

1. iteratee (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the new mapped array.

Example

function square(n) {
  return n * n;
}

_.map(square, [4, 8]);
// => [16, 64]

_.map(square, { 'a': 4, 'b': 8 });
// => [16, 64] (iteration order is not guaranteed)

var users = [
  { 'user': 'barney' },
  { 'user': 'fred' }
];

// The `_.property` iteratee shorthand.
_.map('user', users);
// => ['barney', 'fred']

---

_.orderBy(iteratees, orders, collection)

# Ⓢ Ⓣ Ⓝ

This method is like _.sortBy except that it allows specifying the sort orders of the iteratees to sort by. If orders is unspecified, all values are sorted in ascending order. Otherwise, specify an order of "desc" for descending or "asc" for ascending sort order of corresponding values.

Since

4.0.0

Arguments

1. iteratees (Array[]|Function[]|Object[]|string[]): The iteratees to sort by.
2. orders (string[]): The sort orders of iteratees.
3. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the new sorted array.

Example

var users = [
  { 'user': 'fred',   'age': 48 },
  { 'user': 'barney', 'age': 34 },
  { 'user': 'fred',   'age': 40 },
  { 'user': 'barney', 'age': 36 }
];

// Sort by `user` in ascending order and by `age` in descending order.
_.orderBy(['user', 'age'], ['asc', 'desc'], users);
// => objects for [['barney', 36], ['barney', 34], ['fred', 48], ['fred', 40]]

---

_.partition(predicate, collection)

# Ⓢ Ⓣ Ⓝ

Creates an array of elements split into two groups, the first of which contains elements predicate returns truthy for, the second of which contains elements predicate returns falsey for. The predicate is invoked with one argument: (value).

Since

3.0.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the array of grouped elements.

Example

var users = [
  { 'user': 'barney',  'age': 36, 'active': false },
  { 'user': 'fred',    'age': 40, 'active': true },
  { 'user': 'pebbles', 'age': 1,  'active': false }
];

_.partition(function(o) { return o.active; }, users);
// => objects for [['fred'], ['barney', 'pebbles']]

// The `_.matches` iteratee shorthand.
_.partition({ 'age': 1, 'active': false }, users);
// => objects for [['pebbles'], ['barney', 'fred']]

// The `_.matchesProperty` iteratee shorthand.
_.partition(['active', false], users);
// => objects for [['barney', 'pebbles'], ['fred']]

// The `_.property` iteratee shorthand.
_.partition('active', users);
// => objects for [['fred'], ['barney', 'pebbles']]

---

_.reduce(iteratee, accumulator, collection)

# Ⓢ Ⓣ Ⓝ

Reduces collection to a value which is the accumulated result of running each element in collection thru iteratee, where each successive invocation is supplied the return value of the previous. If accumulator is not given, the first element of collection is used as the initial value. The iteratee is invoked with four arguments:
(accumulator, value, index|key, collection).

Many lodash methods are guarded to work as iteratees for methods like _.reduce, _.reduceRight, and _.transform.

The guarded methods are:
assign, defaults, defaultsDeep, includes, merge, orderBy, and sortBy

Since

0.1.0

Arguments

1. iteratee (Function): The function invoked per iteration.
2. accumulator (*): The initial value.
3. collection (Array|Object): The collection to iterate over.

Returns

(*): Returns the accumulated value.

Example

_.reduce(function(sum, n) {
  return sum + n;
}, 0, [1, 2]);
// => 3

_.reduce(function(result, value, key) {
  (result[value] || (result[value] = [])).push(key);
  return result;
}, {}, { 'a': 1, 'b': 2, 'c': 1 });
// => { '1': ['a', 'c'], '2': ['b'] } (iteration order is not guaranteed)

---

_.reduceRight(iteratee, accumulator, collection)

# Ⓢ Ⓣ Ⓝ

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

Since

0.1.0

Arguments

1. iteratee (Function): The function invoked per iteration.
2. accumulator (*): The initial value.
3. collection (Array|Object): The collection to iterate over.

Returns

(*): Returns the accumulated value.

Example

var array = [[0, 1], [2, 3], [4, 5]];

_.reduceRight(function(flattened, other) {
  return flattened.concat(other);
}, [], array);
// => [4, 5, 2, 3, 0, 1]

---

_.reject(predicate, collection)

# Ⓢ Ⓣ Ⓝ

The opposite of _.filter; this method returns the elements of collection that predicate does not return truthy for.

Since

0.1.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the new filtered array.

Example

var users = [
  { 'user': 'barney', 'age': 36, 'active': false },
  { 'user': 'fred',   'age': 40, 'active': true }
];

_.reject(function(o) { return !o.active; }, users);
// => objects for ['fred']

// The `_.matches` iteratee shorthand.
_.reject({ 'age': 40, 'active': true }, users);
// => objects for ['barney']

// The `_.matchesProperty` iteratee shorthand.
_.reject(['active', false], users);
// => objects for ['fred']

// The `_.property` iteratee shorthand.
_.reject('active', users);
// => objects for ['barney']

---

_.sample(collection)

# Ⓢ Ⓣ Ⓝ

Gets a random element from collection.

Since

2.0.0

Arguments

1. collection (Array|Object): The collection to sample.

Returns

(*): Returns the random element.

Example

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

---

_.sampleSize(n, collection)

# Ⓢ Ⓣ Ⓝ

Gets n random elements at unique keys from collection up to the size of collection.

Since

4.0.0

Arguments

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

Returns

(Array): Returns the random elements.

Example

_.sampleSize(2, [1, 2, 3]);
// => [3, 1]

_.sampleSize(4, [1, 2, 3]);
// => [2, 3, 1]

---

_.shuffle(collection)

# Ⓢ Ⓣ Ⓝ

Creates an array of shuffled values, using a version of the Fisher-Yates shuffle.

Since

0.1.0

Arguments

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

Returns

(Array): Returns the new shuffled array.

Example

_.shuffle([1, 2, 3, 4]);
// => [4, 1, 3, 2]

---

_.size(collection)

# Ⓢ Ⓣ Ⓝ

Gets the size of collection by returning its length for array-like values or the number of own enumerable string keyed properties for objects.

Since

0.1.0

Arguments

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

Returns

(number): Returns the collection size.

Example

_.size([1, 2, 3]);
// => 3

_.size({ 'a': 1, 'b': 2 });
// => 2

_.size('pebbles');
// => 7

---

_.some(predicate, collection)

# Ⓢ Ⓣ Ⓝ

Checks if predicate returns truthy for any element of collection. Iteration is stopped once predicate returns truthy. The predicate is invoked with three arguments: (value, index|key, collection).

Since

0.1.0

Arguments

1. predicate (Function): The function invoked per iteration.
2. collection (Array|Object): The collection to iterate over.

Returns

(boolean): Returns true if any element passes the predicate check, else false.

Example

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

var users = [
  { 'user': 'barney', 'active': true },
  { 'user': 'fred',   'active': false }
];

// The `_.matches` iteratee shorthand.
_.some({ 'user': 'barney', 'active': false }, users);
// => false

// The `_.matchesProperty` iteratee shorthand.
_.some(['active', false], users);
// => true

// The `_.property` iteratee shorthand.
_.some('active', users);
// => true

---

_.sortBy(iteratees, collection)

# Ⓢ Ⓣ Ⓝ

Creates an array of elements, sorted in ascending order by the results of running each element in a collection thru each iteratee. This method performs a stable sort, that is, it preserves the original sort order of equal elements. The iteratees are invoked with one argument: (value).

Since

0.1.0

Arguments

1. iteratees (Function|Function[]): The iteratees to sort by.
2. collection (Array|Object): The collection to iterate over.

Returns

(Array): Returns the new sorted array.

Example

var users = [
  { 'user': 'fred',   'age': 48 },
  { 'user': 'barney', 'age': 36 },
  { 'user': 'fred',   'age': 30 },
  { 'user': 'barney', 'age': 34 }
];

_.sortBy([function(o) { return o.user; }], users);
// => objects for [['barney', 36], ['barney', 34], ['fred', 48], ['fred', 30]]

_.sortBy(['user', 'age'], users);
// => objects for [['barney', 34], ['barney', 36], ['fred', 30], ['fred', 48]]

---

“Date” Methods

_.now()

# Ⓢ Ⓣ Ⓝ

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

Since

2.4.0

Returns

(number): Returns the timestamp.

Example

_.defer([function(stamp) {
  console.log(_.now(null) - stamp);
}, _.now()]);
// => Logs the number of milliseconds it took for the deferred invocation.

---

“Function” Methods

_.after(func, n)

# Ⓢ Ⓣ Ⓝ

The opposite of _.before; this method creates a function that invokes func once it's called n or more times.

Since

0.1.0

Arguments

1. func (Function): The function to restrict.
2. n (number): The number of calls before func is invoked.

Returns

(Function): Returns the new restricted function.

Example

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

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

_.forEach(function(type) {
  asyncSave({ 'type': type, 'complete': done });
}, saves);
// => Logs 'done saving!' after the two async saves have completed.

---

_.ary(n, func)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func, with up to n arguments, ignoring any additional arguments.

Since

3.0.0

Arguments

1. n (number): The arity cap.
2. func (Function): The function to cap arguments for.

Returns

(Function): Returns the new capped function.

Example

_.map(_.ary(parseInt, 1), ['6', '8', '10']);
// => [6, 8, 10]

---

_.before(func, n)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func, with the this binding and arguments of the created function, while it's called less than n times. Subsequent calls to the created function return the result of the last func invocation.

Since

3.0.0

Arguments

1. func (Function): The function to restrict.
2. n (number): The number of calls at which func is no longer invoked.

Returns

(Function): Returns the new restricted function.

Example

jQuery(element).on('click', _.before(addContactToList, 5));
// => Allows adding up to 4 contacts to the list.

---

_.bind(func, thisArg)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func with the this binding of thisArg and partials prepended to the arguments it receives.

The _.bind.placeholder value, which defaults to _ in monolithic builds, may be used as a placeholder for partially applied arguments.

Note: Unlike native Function#bind, this method doesn't set the "length" property of bound functions.

Since

0.1.0

Arguments

1. func (Function): The function to bind.
2. thisArg (*): The this binding of func.

Returns

(Function): Returns the new bound function.

Example

function greet(greeting, punctuation) {
  return greeting + ' ' + this.user + punctuation;
}

var object = { 'user': 'fred' };

var bound = _.bind(greet, [object, 'hi']);
bound('!');
// => 'hi fred!'

// Bound with placeholders.
var bound = _.bind(greet, [object, _, '!']);
bound('hi');
// => 'hi fred!'

---

_.bindKey(object, key)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes the method at object[key] with partials prepended to the arguments it receives.

This method differs from _.bind by allowing bound functions to reference methods that may be redefined or don't yet exist. See Peter Michaux's article for more details.

The _.bindKey.placeholder value, which defaults to _ in monolithic builds, may be used as a placeholder for partially applied arguments.

Since

0.10.0

Arguments

1. object (Object): The object to invoke the method on.
2. key (string): The key of the method.

Returns

(Function): Returns the new bound function.

Example

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

var bound = _.bindKey(object, ['greet', 'hi']);
bound('!');
// => 'hi fred!'

object.greet = function(greeting, punctuation) {
  return greeting + 'ya ' + this.user + punctuation;
};

bound('!');
// => 'hiya fred!'

// Bound with placeholders.
var bound = _.bindKey(object, ['greet', _, '!']);
bound('hi');
// => 'hiya fred!'

---

_.curry(func)

# Ⓢ Ⓣ Ⓝ

Creates a function that accepts arguments of func and either invokes func returning its result, if at least arity number of arguments have been provided, or returns a function that accepts the remaining func arguments, and so on. The arity of func may be specified if func.length is not sufficient.

The _.curry.placeholder value, which defaults to _ in monolithic builds, may be used as a placeholder for provided arguments.

Note: This method doesn't set the "length" property of curried functions.

Since

2.0.0

Arguments

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

Returns

(Function): Returns the new curried function.

Example

var abc = function(a, b, c) {
  return [a, b, c];
};

var curried = _.curry(abc);

curried(1)(2)(3);
// => [1, 2, 3]

curried(1, 2)(3);
// => [1, 2, 3]

curried(1, 2, 3);
// => [1, 2, 3]

// Curried with placeholders.
curried(1)(_, 3)(2);
// => [1, 2, 3]

---

_.curryRight(func)

# Ⓢ Ⓣ Ⓝ

This method is like _.curry except that arguments are applied to func in the manner of _.partialRight instead of _.partial.

The _.curryRight.placeholder value, which defaults to _ in monolithic builds, may be used as a placeholder for provided arguments.

Note: This method doesn't set the "length" property of curried functions.

Since

3.0.0

Arguments

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

Returns

(Function): Returns the new curried function.

Example

var abc = function(a, b, c) {
  return [a, b, c];
};

var curried = _.curryRight(abc);

curried(3)(2)(1);
// => [1, 2, 3]

curried(2, 3)(1);
// => [1, 2, 3]

curried(1, 2, 3);
// => [1, 2, 3]

// Curried with placeholders.
curried(3)(1, _)(2);
// => [1, 2, 3]

---

_.debounce(wait, func)

# Ⓢ Ⓣ Ⓝ

Creates a debounced function that delays invoking func until after wait milliseconds have elapsed since the last time the debounced function was invoked. The debounced function comes with a cancel method to cancel delayed func invocations and a flush method to immediately invoke them. Provide options to indicate whether func should be invoked on the leading and/or trailing edge of the wait timeout. The func is invoked with the last arguments provided to the debounced function. Subsequent calls to the debounced function return the result of the last func invocation.

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

If wait is 0 and leading is false, func invocation is deferred until to the next tick, similar to setTimeout with a timeout of 0.

See David Corbacho's article for details over the differences between _.debounce and _.throttle.

Since

0.1.0

Arguments

1. wait (number): The number of milliseconds to delay.
2. func (Function): The function to debounce.

Returns

(Function): Returns the new debounced function.

Example

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

// Invoke `sendMail` when clicked, debouncing subsequent calls.
jQuery(element).on('click', _.debounce([300, {
  'leading': true,
  'trailing': false
}], sendMail));

// Ensure `batchLog` is invoked once after 1 second of debounced calls.
var debounced = _.debounce([250, { 'maxWait': 1000 }], batchLog);
var source = new EventSource('/stream');
jQuery(source).on('message', debounced);

// Cancel the trailing debounced invocation.
jQuery(window).on('popstate', debounced.cancel);

---

_.defer(func)

# Ⓢ Ⓣ Ⓝ

Defers invoking the func until the current call stack has cleared. Any additional arguments are provided to func when it's invoked.

Since

0.1.0

Arguments

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

Returns

(number): Returns the timer id.

Example

_.defer([function(text) {
  console.log(text);
}, 'deferred']);
// => Logs 'deferred' after one millisecond.

---

_.delay(wait, func)

# Ⓢ Ⓣ Ⓝ

Invokes func after wait milliseconds. Any additional arguments are provided to func when it's invoked.

Since

0.1.0

Arguments

1. wait (number): The number of milliseconds to delay invocation.
2. func (Function): The function to delay.

Returns

(number): Returns the timer id.

Example

_.delay([1000, 'later'], function(text) {
  console.log(text);
});
// => Logs 'later' after one second.

---

_.flip(func)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func with arguments reversed.

Since

4.0.0

Arguments

1. func (Function): The function to flip arguments for.

Returns

(Function): Returns the new flipped function.

Example

var flipped = _.flip(function() {
  return _.toArray(arguments);
});

flipped('a', 'b', 'c', 'd');
// => ['d', 'c', 'b', 'a']

---

_.memoize(func)

# Ⓢ Ⓣ Ⓝ

Creates a function that memoizes the result of func. If resolver is provided, it determines 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 map cache key. The func is invoked with the this binding of the memoized function.

Note: The cache is exposed as the cache property on the memoized function. Its creation may be customized by replacing the _.memoize.Cache constructor with one whose instances implement the Map method interface of clear, delete, get, has, and set.

Since

0.1.0

Arguments

1. func (Function): The function to have its output memoized.

Returns

(Function): Returns the new memoized function.

Example

var object = { 'a': 1, 'b': 2 };
var other = { 'c': 3, 'd': 4 };

var values = _.memoize(_.values);
values(object);
// => [1, 2]

values(other);
// => [3, 4]

object.a = 2;
values(object);
// => [1, 2]

// Modify the result cache.
values.cache.set(object, ['a', 'b']);
values(object);
// => ['a', 'b']

// Replace `_.memoize.Cache`.
_.memoize.Cache = WeakMap;

---

_.negate(predicate)

# Ⓢ Ⓣ Ⓝ

Creates a function that negates the result of the predicate func. The func predicate is invoked with the this binding and arguments of the created function.

Since

3.0.0

Arguments

1. predicate (Function): The predicate to negate.

Returns

(Function): Returns the new negated function.

Example

function isEven(n) {
  return n % 2 == 0;
}

_.filter(_.negate(isEven), [1, 2, 3, 4, 5, 6]);
// => [1, 3, 5]

---

_.once(func)

# Ⓢ Ⓣ Ⓝ

Creates a function that is restricted to invoking func once. Repeat calls to the function return the value of the first invocation. The func is invoked with the this binding and arguments of the created function.

Since

0.1.0

Arguments

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

Returns

(Function): Returns the new restricted function.

Example

var initialize = _.once(createApplication);
initialize();
initialize();
// => `createApplication` is invoked once

---

_.overArgs(func, transforms)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func with its arguments transformed.

Since

4.0.0

Arguments

1. func (Function): The function to wrap.
2. transforms (Function|Function[]): The argument transforms.

Returns

(Function): Returns the new function.

Example

function doubled(n) {
  return n * 2;
}

function square(n) {
  return n * n;
}

var func = _.overArgs(function(x, y) {
  return [x, y];
}, [square, doubled]);

func(9, 3);
// => [81, 6]

func(10, 5);
// => [100, 10]

---

_.partial(func, partials)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func with partials prepended to the arguments it receives. This method is like _.bind except it does not alter the this binding.

The _.partial.placeholder value, which defaults to _ in monolithic builds, may be used as a placeholder for partially applied arguments.

Note: This method doesn't set the "length" property of partially applied functions.

Since

0.2.0

Arguments

1. func (Function): The function to partially apply arguments to.
2. partials (*|*[]): The arguments to be partially applied.

Returns

(Function): Returns the new partially applied function.

Example

function greet(greeting, name) {
  return greeting + ' ' + name;
}

var sayHelloTo = _.partial(greet, 'hello');
sayHelloTo('fred');
// => 'hello fred'

// Partially applied with placeholders.
var greetFred = _.partial(greet, [_, 'fred']);
greetFred('hi');
// => 'hi fred'

---

_.partialRight(func, partials)

# Ⓢ Ⓣ Ⓝ

This method is like _.partial except that partially applied arguments are appended to the arguments it receives.

The _.partialRight.placeholder value, which defaults to _ in monolithic builds, may be used as a placeholder for partially applied arguments.

Note: This method doesn't set the "length" property of partially applied functions.

Since

1.0.0

Arguments

1. func (Function): The function to partially apply arguments to.
2. partials (*|*[]): The arguments to be partially applied.

Returns

(Function): Returns the new partially applied function.

Example

function greet(greeting, name) {
  return greeting + ' ' + name;
}

var greetFred = _.partialRight(greet, 'fred');
greetFred('hi');
// => 'hi fred'

// Partially applied with placeholders.
var sayHelloTo = _.partialRight(greet, ['hello', _]);
sayHelloTo('fred');
// => 'hello fred'

---

_.rearg(indexes, func)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func with arguments arranged according to the specified indexes where the argument value at the first index is provided as the first argument, the argument value at the second index is provided as the second argument, and so on.

Since

3.0.0

Arguments

1. indexes (number|number[]): The arranged argument indexes.
2. func (Function): The function to rearrange arguments for.

Returns

(Function): Returns the new function.

Example

var rearged = _.rearg([2, 0, 1], function(a, b, c) {
  return [a, b, c];
});

rearged('b', 'c', 'a')
// => ['a', 'b', 'c']

---

_.rest(func)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func with the this binding of the created function and arguments from start and beyond provided as an array.

Note: This method is based on the rest parameter.

Since

4.0.0

Arguments

1. func (Function): The function to apply a rest parameter to.

Returns

(Function): Returns the new function.

Example

var say = _.rest(function(what, names) {
  return what + ' ' + _.initial(names).join(', ') +
    (_.size(names) > 1 ? ', & ' : '') + _.last(names);
});

say('hello', 'fred', 'barney', 'pebbles');
// => 'hello fred, barney, & pebbles'

---

_.spread(func)

# Ⓢ Ⓣ Ⓝ

Creates a function that invokes func with the this binding of the create function and an array of arguments much like Function#apply.

Note: This method is based on the spread operator.

Since

3.2.0

Arguments

1. func (Function): The function to spread arguments over.

Returns

(Function): Returns the new function.

Example

var say = _.spread(function(who, what) {
  return who + ' says ' + what;
});

say(['fred', 'hello']);
// => 'fred says hello'

var numbers = Promise.all([
  Promise.resolve(40),
  Promise.resolve(36)
]);

numbers.then(_.spread(function(x, y) {
  return x + y;
}));
// => a Promise of 76

---

_.throttle(wait, func)

# Ⓢ Ⓣ Ⓝ

Creates a throttled function that only invokes func at most once per every wait milliseconds. The throttled function comes with a cancel method to cancel delayed func invocations and a flush method to immediately invoke them. Provide options to indicate whether func should be invoked on the leading and/or trailing edge of the wait timeout. The func is invoked with the last arguments provided to the throttled function. Subsequent calls to the throttled function return the result of the last func invocation.

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

If wait is 0 and leading is false, func invocation is deferred until to the next tick, similar to setTimeout with a timeout of 0.

See David Corbacho's article for details over the differences between _.throttle and _.debounce.

Since

0.1.0

Arguments

1. wait (number): The number of milliseconds to throttle invocations to.
2. func (Function): The function to throttle.

Returns

(Function): Returns the new throttled function.

Example

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

// Invoke `renewToken` when the click event is fired, but not more than once every 5 minutes.
var throttled = _.throttle([300000, { 'trailing': false }], renewToken);
jQuery(element).on('click', throttled);

// Cancel the trailing throttled invocation.
jQuery(window).on('popstate', throttled.cancel);

---

_.unary(func)

# Ⓢ Ⓣ Ⓝ

Creates a function that accepts up to one argument, ignoring any additional arguments.

Since

4.0.0

Arguments

1. func (Function): The function to cap arguments for.

Returns

(Function): Returns the new capped function.

Example

_.map(_.unary(parseInt), ['6', '8', '10']);
// => [6, 8, 10]

---

_.wrap(wrapper, value)

# Ⓢ Ⓣ Ⓝ

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

Since

0.1.0

Arguments

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

Returns

(Function): Returns the new function.

Example

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

p('fred, barney, & pebbles');
// => '<p>fred, barney, &amp; pebbles</p>'

---

“Lang” Methods

_.castArray(value)

# Ⓢ Ⓣ Ⓝ

Casts value as an array if it's not one.

Since

4.4.0

Arguments

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

Returns

(Array): Returns the cast array.

Example

_.castArray(1);
// => [1]

_.castArray({ 'a': 1 });
// => [{ 'a': 1 }]

_.castArray('abc');
// => ['abc']

_.castArray(null);
// => [null]

_.castArray(undefined);
// => [undefined]

_.castArray(null);
// => []

var array = [1, 2, 3];
// => true

---

_.clone(value)

# Ⓢ Ⓣ Ⓝ

Creates a shallow clone of value.

Note: This method is loosely based on the structured clone algorithm and supports cloning arrays, array buffers, booleans, date objects, maps, numbers, Object objects, regexes, sets, strings, symbols, and typed arrays. The own enumerable properties of arguments objects are cloned as plain objects. An empty object is returned for uncloneable values such as error objects, functions, DOM nodes, and WeakMaps.

Since

0.1.0

Arguments

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

Returns

(*): Returns the cloned value.

Example

var objects = [{ 'a': 1 }, { 'b': 2 }];

var shallow = _.clone(objects);
// => true

---

_.cloneDeep(value)

# Ⓢ Ⓣ Ⓝ

This method is like _.clone except that it recursively clones value.

Since

1.0.0

Arguments

1. value (*): The value to recursively clone.

Returns

(*): Returns the deep cloned value.

Example

var objects = [{ 'a': 1 }, { 'b': 2 }];

var deep = _.cloneDeep(objects);
// => false

---

_.cloneDeepWith(customizer, value)

# Ⓢ Ⓣ Ⓝ

This method is like _.cloneWith except that it recursively clones value.

Since

4.0.0

Arguments

1. customizer (Function): The function to customize cloning.
2. value (*): The value to recursively clone.

Returns

(*): Returns the deep cloned value.

Example

function customizer(value) {
  if (_.isElement(value)) {
    return value.cloneNode(true);
  }
}

var el = _.cloneDeepWith(customizer, document.body);

// => false
// => 'BODY'
// => 20

---

_.cloneWith(customizer, value)

# Ⓢ Ⓣ Ⓝ

This method is like _.clone except that it accepts customizer which is invoked to produce the cloned value. If customizer returns undefined, cloning is handled by the method instead. The customizer is invoked with up to four arguments; (value [, index|key, object, stack]).

Since

4.0.0

Arguments

1. customizer (Function): The function to customize cloning.
2. value (*): The value to clone.

Returns

(*): Returns the cloned value.

Example

function customizer(value) {
  if (_.isElement(value)) {
    return value.cloneNode(false);
  }
}

var el = _.cloneWith(customizer, document.body);

// => false
// => 'BODY'
// => 0

---

_.conformsTo(source, object)

# Ⓢ Ⓣ Ⓝ

Checks if object conforms to source by invoking the predicate properties of source with the corresponding property values of object.

Note: This method is equivalent to _.conforms when source is partially applied.

Since

4.14.0

Arguments

1. source (Object): The object of property predicates to conform to.
2. object (Object): The object to inspect.

Returns

(boolean): Returns true if object conforms, else false.

Example

var object = { 'a': 1, 'b': 2 };

_.conformsTo({ 'b': function(n) { return n > 1; } }, object);
// => true

_.conformsTo({ 'b': function(n) { return n > 2; } }, object);
// => false

---

_.eq(value, other)

# Ⓢ Ⓣ Ⓝ

Performs a SameValueZero comparison between two values to determine if they are equivalent.

Since

4.0.0

Arguments

1. value (*): The value to compare.
2. other (*): The other value to compare.

Returns

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

Example

var object = { 'a': 1 };
var other = { 'a': 1 };

_.eq(object, object);
// => true

_.eq(object, other);
// => false

_.eq('a', 'a');
// => true

_.eq('a', Object('a'));
// => false

_.eq(NaN, NaN);
// => true

---

_.gt(value, other)

# Ⓢ Ⓣ Ⓝ

Checks if value is greater than other.

Since

3.9.0

Arguments

1. value (*): The value to compare.
2. other (*): The other value to compare.

Returns

(boolean): Returns true if value is greater than other, else false.

Example

_.gt(3, 1);
// => true

_.gt(3, 3);
// => false

_.gt(1, 3);
// => false

---

_.gte(value, other)

# Ⓢ Ⓣ Ⓝ

Checks if value is greater than or equal to other.

Since

3.9.0

Arguments

1. value (*): The value to compare.
2. other (*): The other value to compare.

Returns

(boolean): Returns true if value is greater than or equal to other, else false.

Example

_.gte(3, 1);
// => true

_.gte(3, 3);
// => true

_.gte(1, 3);
// => false

---

_.isArguments(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is likely an arguments object.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isArguments(function() { return arguments; }());
// => true

_.isArguments([1, 2, 3]);
// => false

---

_.isArray(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is classified as an Array object.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isArray([1, 2, 3]);
// => true

_.isArray(document.body.children);
// => false

_.isArray('abc');
// => false

_.isArray(_.noop);
// => false

---

_.isArrayBuffer(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is classified as an ArrayBuffer object.

Since

4.3.0

Arguments

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

Returns

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

Example

_.isArrayBuffer(new ArrayBuffer(2));
// => true

_.isArrayBuffer(new Array(2));
// => false

---

_.isArrayLike(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is array-like. A value is considered array-like if it's not a function and has a value.length that's an integer greater than or equal to 0 and less than or equal to Number.MAX_SAFE_INTEGER.

Since

4.0.0

Arguments

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

Returns

(boolean): Returns true if value is array-like, else false.

Example

_.isArrayLike([1, 2, 3]);
// => true

_.isArrayLike(document.body.children);
// => true

_.isArrayLike('abc');
// => true

_.isArrayLike(_.noop);
// => false

---

_.isArrayLikeObject(value)

# Ⓢ Ⓣ Ⓝ

This method is like _.isArrayLike except that it also checks if value is an object.

Since

4.0.0

Arguments

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

Returns

(boolean): Returns true if value is an array-like object, else false.

Example

_.isArrayLikeObject([1, 2, 3]);
// => true

_.isArrayLikeObject(document.body.children);
// => true

_.isArrayLikeObject('abc');
// => false

_.isArrayLikeObject(_.noop);
// => false

---

_.isBoolean(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is classified as a boolean primitive or object.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isBoolean(false);
// => true

_.isBoolean(null);
// => false

---

_.isBuffer(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is a buffer.

Since

4.3.0

Arguments

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

Returns

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

Example

_.isBuffer(new Buffer(2));
// => true

_.isBuffer(new Uint8Array(2));
// => false

---

_.isDate(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is classified as a Date object.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isDate(new Date);
// => true

_.isDate('Mon April 23 2012');
// => false

---

_.isElement(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is likely a DOM element.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isElement(document.body);
// => true

_.isElement('<body>');
// => false

---

_.isEmpty(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is an empty object, collection, map, or set.

Objects are considered empty if they have no own enumerable string keyed properties.

Array-like values such as arguments objects, arrays, buffers, strings, or jQuery-like collections are considered empty if they have a length of 0. Similarly, maps and sets are considered empty if they have a size of 0.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isEmpty(null);
// => true

_.isEmpty(true);
// => true

_.isEmpty(1);
// => true

_.isEmpty([1, 2, 3]);
// => false

_.isEmpty({ 'a': 1 });
// => false

---

_.isEqual(value, other)

# Ⓢ Ⓣ Ⓝ

Performs a deep comparison between two values to determine if they are equivalent.

Note: This method supports comparing arrays, array buffers, booleans, date objects, error objects, maps, numbers, Object objects, regexes, sets, strings, symbols, and typed arrays. Object objects are compared by their own, not inherited, enumerable properties. Functions and DOM nodes are compared by strict equality, i.e. ===.

Since

0.1.0

Arguments

1. value (*): The value to compare.
2. other (*): The other value to compare.

Returns

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

Example

var object = { 'a': 1 };
var other = { 'a': 1 };

_.isEqual(object, other);
// => true

object === other;
// => false

---

_.isEqualWith(customizer, value, other)

# Ⓢ Ⓣ Ⓝ

This method is like _.isEqual except that it accepts customizer which is invoked to compare values. If customizer returns undefined, comparisons are handled by the method instead. The customizer is invoked with up to six arguments: (objValue, othValue [, index|key, object, other, stack]).

Since

4.0.0

Arguments

1. customizer (Function): The function to customize comparisons.
2. value (*): The value to compare.
3. other (*): The other value to compare.

Returns

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

Example

function isGreeting(value) {
  return /^h(?:i|ello)$/.test(value);
}

function customizer(objValue, othValue) {
  if (isGreeting(objValue) && isGreeting(othValue)) {
    return true;
  }
}

var array = ['hello', 'goodbye'];
var other = ['hi', 'goodbye'];

_.isEqualWith(customizer, array, other);
// => true

---

_.isError(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is an Error, EvalError, RangeError, ReferenceError, SyntaxError, TypeError, or URIError object.

Since

3.0.0

Arguments

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

Returns

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

Example

_.isError(new Error);
// => true

_.isError(Error);
// => false

---

_.isFinite(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is a finite primitive number.

Note: This method is based on Number.isFinite.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isFinite(3);
// => true

_.isFinite(Number.MIN_VALUE);
// => true

_.isFinite(Infinity);
// => false

_.isFinite('3');
// => false

---

_.isFunction(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is classified as a Function object.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isFunction(_);
// => true

_.isFunction(/abc/);
// => false

---

_.isInteger(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is an integer.

Note: This method is based on Number.isInteger.

Since

4.0.0

Arguments

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

Returns

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

Example

_.isInteger(3);
// => true

_.isInteger(Number.MIN_VALUE);
// => false

_.isInteger(Infinity);
// => false

_.isInteger('3');
// => false

---

_.isLength(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is a valid array-like length.

Note: This method is loosely based on ToLength.

Since

4.0.0

Arguments

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

Returns

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

Example

_.isLength(3);
// => true

_.isLength(Number.MIN_VALUE);
// => false

_.isLength(Infinity);
// => false

_.isLength('3');
// => false

---

_.isMap(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is classified as a Map object.

Since

4.3.0

Arguments

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

Returns

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

Example

_.isMap(new Map);
// => true

_.isMap(new WeakMap);
// => false

---

_.isMatch(source, object)

# Ⓢ Ⓣ Ⓝ

Performs a partial deep comparison between object and source to determine if object contains equivalent property values.

Note: This method is equivalent to _.matches when source is partially applied.

Partial comparisons will match empty array and empty object source values against any array or object value, respectively. See _.isEqual for a list of supported value comparisons.

Since

3.0.0

Arguments

1. source (Object): The object of property values to match.
2. object (Object): The object to inspect.

Returns

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

Example

var object = { 'a': 1, 'b': 2 };

_.isMatch({ 'b': 2 }, object);
// => true

_.isMatch({ 'b': 1 }, object);
// => false

---

_.isMatchWith(customizer, source, object)

# Ⓢ Ⓣ Ⓝ

This method is like _.isMatch except that it accepts customizer which is invoked to compare values. If customizer returns undefined, comparisons are handled by the method instead. The customizer is invoked with five arguments: (objValue, srcValue, index|key, object, source).

Since

4.0.0

Arguments

1. customizer (Function): The function to customize comparisons.
2. source (Object): The object of property values to match.
3. object (Object): The object to inspect.

Returns

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

Example

function isGreeting(value) {
  return /^h(?:i|ello)$/.test(value);
}

function customizer(objValue, srcValue) {
  if (isGreeting(objValue) && isGreeting(srcValue)) {
    return true;
  }
}

var object = { 'greeting': 'hello' };
var source = { 'greeting': 'hi' };

_.isMatchWith(customizer, source, object);
// => true

---

_.isNaN(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is NaN.

Note: This method is based on Number.isNaN and is not the same as global isNaN which returns true for undefined and other non-number values.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isNaN(NaN);
// => true

_.isNaN(new Number(NaN));
// => true

isNaN(undefined);
// => true

_.isNaN(undefined);
// => false

---

_.isNative(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is a pristine native function.

Note: This method can't reliably detect native functions in the presence of the core-js package because core-js circumvents this kind of detection. Despite multiple requests, the core-js maintainer has made it clear: any attempt to fix the detection will be obstructed. As a result, we're left with little choice but to throw an error. Unfortunately, this also affects packages, like babel-polyfill, which rely on core-js.

Since

3.0.0

Arguments

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

Returns

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

Example

_.isNative(Array.prototype.push);
// => true

_.isNative(_);
// => false

---

_.isNil(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is null or undefined.

Since

4.0.0

Arguments

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

Returns

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

Example

_.isNil(null);
// => true

_.isNil(void 0);
// => true

_.isNil(NaN);
// => false

---

_.isNull(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is null.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isNull(null);
// => true

_.isNull(void 0);
// => false

---

_.isNumber(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is classified as a Number primitive or object.

Note: To exclude Infinity, -Infinity, and NaN, which are classified as numbers, use the _.isFinite method.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isNumber(3);
// => true

_.isNumber(Number.MIN_VALUE);
// => true

_.isNumber(Infinity);
// => true

_.isNumber('3');
// => false

---

_.isObject(value)

# Ⓢ Ⓣ Ⓝ

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

Since

0.1.0

Arguments

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

Returns

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

Example

_.isObject({});
// => true

_.isObject([1, 2, 3]);
// => true

_.isObject(_.noop);
// => true

_.isObject(null);
// => false

---

_.isObjectLike(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is object-like. A value is object-like if it's not null and has a typeof result of "object".

Since

4.0.0

Arguments

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

Returns

(boolean): Returns true if value is object-like, else false.

Example

_.isObjectLike({});
// => true

_.isObjectLike([1, 2, 3]);
// => true

_.isObjectLike(_.noop);
// => false

_.isObjectLike(null);
// => false

---

_.isPlainObject(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is a plain object, that is, an object created by the Object constructor or one with a [[Prototype]] of null.

Since

0.8.0

Arguments

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

Returns

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

Example

function Foo() {
  this.a = 1;
}

_.isPlainObject(new Foo);
// => false

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

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

_.isPlainObject(Object.create(null));
// => true

---

_.isRegExp(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is classified as a RegExp object.

Since

0.1.0

Arguments

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

Returns

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

Example

_.isRegExp(/abc/);
// => true

_.isRegExp('/abc/');
// => false

---

_.isSafeInteger(value)

# Ⓢ Ⓣ Ⓝ

Checks if value is a safe integer. An integer is safe if it's an IEEE-754 double precision number which isn't the result o