37 Common JS Utility Functions [Lodash]

Array

chunk

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.

Arguments

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

Returns

(Array): Returns the new array of chunks.

Example

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

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

compact

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

Arguments

array (Array): The array to compact.

Returns

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

Examples

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

concat

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

Arguments

array (Array): The array to concatenate. [values] (...x): The values to concatenate.

Returns

(Array): Returns the new concatenated array.

Example

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

console.log(other);
// => [1, 2, 3, [4]]

console.log(array);
// => [1]

dropRight

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

Arguments

array (Array): The array to query. [n=1] (number): The number of elements to drop.

Returns

(Array): Returns the slice of array.

Examples

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

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

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

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

head

Gets the first element of array.

Arguments

array (Array): The array to query.

Returns

(x): Returns the first element of array.

Example

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

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

indexOf

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.

Arguments

array (Array): The array to inspect. value (x): The value to search for. [fromIndex=0] (number): The index to search from.

Returns

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

Example

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

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

initial

Gets all but the last element of array.

Arguments

array (Array): The array to query.

Returns

(Array): Returns the slice of array.

Examples

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

join

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

Arguments

array (Array): The array to convert. [separator=','] (string): The element separator.

Returns

(string): Returns the joined string.

Example

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

nth

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

Arguments

array (Array): The array to query. [n=0] (number): The index of the element to return.

Returns

(x): Returns the nth element of array.

Examples

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

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

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

pull

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

Note: Unlike .without, this method mutates array. Use .remove to remove elements from an array by predicate.

Arguments

array (Array): The array to modify. [values] (...x): The values to remove.

Returns

(Array): Returns array.

Example

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

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

pullAll

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

Note: Unlike difference, this method mutates array.

Arguments

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

Returns

(Array): Returns array.

Examples

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

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

pullAt

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

Note: Unlike at, this method mutates array.

Arguments

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

Returns

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

Examples

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

console.log(array);
// => ['a', 'c']

console.log(pulled);
// => ['b', 'd']

reverse

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

Arguments

array (Array): The array to modify.

Returns

(Array): Returns array.

Example

var array = [1, 2, 3];

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

console.log(array);
// => [3, 2, 1]

slice

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.

Arguments

array (Array): The array to slice. [start=0] (number): The start position. [end=array.length] (number): The end position.

Returns

(Array): Returns the slice of array.

Example

var a = ['zero', 'one', 'two', 'three'];
var sliced = a.slice(1, 3);

console.log(a);      // ['zero', 'one', 'two', 'three']
console.log(sliced); // ['one', 'two']

Lang

isBoolean

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

Arguments

value (x): The value to check.

Returns

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

Example

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

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

isEqual

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

Arguments

value (x): The value to compare. other (x): 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

isNull

Checks if value is null.

Arguments

value (x): The value to check.

Returns

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

Example

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

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

Math

add

Adds two numbers

Arguments

augend (number): The first number in an addition. addend (number): The second number in an addition.

Returns

(number): Returns the total.

Example

_.add(6, 4);
// => 10

divide

Divides two numbers

Arguments

dividend (number): The first number in a division. divisor (number): The second number in a division.

Returns

(number): Returns the quotient.

Example

_.divide(6, 4);
// => 1.5

max

Computes the maximum value of array. If array is empty or falsey, undefined is returned.

Arguments

array (Array): The array to iterate over.

Returns

(x): Returns the maximum value.

Example

_.max([4, 2, 8, 6]);
// => 8

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

maxBy

This method is like .max except that it accepts iteratee which is invoked for each element in array to generate the criterion by which the value is ranked. The iteratee is invoked with one argument: (value).

Arguments

array (Array): The array to iterate over. [iteratee=.identity] (Function): The iteratee invoked per element.

Returns

Returns the maximum value.

Example

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

_.maxBy(objects, function(o) { return o.n; });
// => { 'n': 2 }

// The `_.property` iteratee shorthand.
_.maxBy(objects, 'n');
// => { 'n': 2 }

mean

Computes the mean of the values in array.

Arguments

array (Array): The array to iterate over.

Returns

(number): Returns the mean.

Example

_.mean([4, 2, 8, 6]);
// => 5

min

Computes the minimum value of array. If array is empty or falsey, undefined is returned.

Arguments

array (Array): The array to iterate over.

Returns

(x): Returns the minimum value.

Example

_.min([4, 2, 8, 6]);
// => 2

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

multiply

Multiply two numbers.

Arguments

multiplier (number): The first number in a multiplication. multiplicand (number): The second number in a multiplication.

Returns

(number): Returns the product.

Example

_.multiply(6, 4);
// => 24

subtract

Subtract two numbers.

Arguments

minuend (number): The first number in a subtraction. subtrahend (number): The second number in a subtraction.

Returns

(number): Returns the difference.

Example

_.subtract(6, 4);
// => 2

sum

Computes the sum of the values in array.

Arguments

array (Array): The array to iterate over.

Returns

(number): Returns the sum.

Example

_.sum([4, 2, 8, 6]);
// => 20

string

startsWith

Checks if string starts with the given target string.

Arguments

[string=''] (string): The string to inspect. [target] (string): The string to search for. [position=0] (number): The position to search from.

Returns

(boolean): Returns true if string starts with target, else false.

Example

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

_.startsWith('abc', 'b');
// => false

_.startsWith('abc', 'b', 1);
// => true

trim

Removes leading and trailing whitespace or specified characters from string.

Arguments

[string=''] (string): The string to trim. [chars=whitespace] (string): The characters to trim.

Returns

(string): Returns the trimmed string.

Example

_.trim('  abc  ');
// => 'abc'

_.trim('-_-abc-_-', '_-');
// => 'abc'

_.map(['  foo  ', '  bar  '], _.trim);
// => ['foo', 'bar']