Array Methods Cheat Sheet
Definition: Adds one or more elements to the end of an array and returns the new length of the array.Syntax: array.push(element1[, ...[, elementN]])Example:
let arr = [ 1 , 2 , 3 ] ;
arr . push ( 4 , 5 ) ;
console . log ( arr ) ; // Output: [1, 2, 3, 4, 5]
Definition: Removes the last element from an array and returns that element.Syntax: array.pop()Example:
let arr = [ 1 , 2 , 3 ] ;
let removedElement = arr . pop ( ) ;
console . log ( removedElement ) ; // Output: 3
console . log ( arr ) ; // Output: [1, 2]
Definition: Removes the first element from an array and returns that element.Syntax: array.shift()Example:
let arr = [ 1 , 2 , 3 ] ;
let shiftedElement = arr . shift ( ) ;
console . log ( shiftedElement ) ; // Output: 1
console . log ( arr ) ; // Output: [2, 3]
Definition: Adds one or more elements to the beginning of an array and returns the new length of the array.Syntax: array.unshift(element1[, ...[, elementN]])Example:
let arr = [ 2 , 3 ] ;
arr . unshift ( 0 , 1 ) ;
console . log ( arr ) ; // Output: [0, 1, 2, 3]
Definition: Returns a new array comprised of the array on which it is called joined with the array(s) and/or value(s) provided as arguments.Syntax: array.concat(value1[, value2[, ...[, valueN]]])Example:
let arr1 = [ 1 , 2 ] ;
let arr2 = [ 3 , 4 ] ;
let newArr = arr1 . concat ( arr2 ) ;
console . log ( newArr ) ; // Output: [1, 2, 3, 4]
Definition: Returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included) where begin and end represent the index of items in that array.Syntax: array.slice(begin[, end])Example:
let arr = [ 1 , 2 , 3 , 4 , 5 ] ;
let newArr = arr . slice ( 1 , 3 ) ;
console . log ( newArr ) ; // Output: [2, 3]
Definition: Changes the contents of an array by removing or replacing existing elements and/or adding new elements in place.Syntax: array.splice(start[, deleteCount[, item1[, item2[, ...]]]])Example:
let arr = [ 1 , 2 , 3 , 4 , 5 ] ;
arr . splice ( 1 , 2 , 'a' , 'b' ) ;
console . log ( arr ) ; // Output: [1, 'a', 'b', 4, 5]
Definition: Executes a provided function once for each array element.Syntax: array.forEach(callback(currentValue [, index [, array]])[, thisArg])Example:
let arr = [ 1 , 2 , 3 ] ;
arr . forEach ( element => console . log ( element * 2 ) ) ;
// Output:
// 2
// 4
// 6
Definition: Creates a new array populated with the results of calling a provided function on every element in the calling array.Syntax: array.map(callback(currentValue [, index [, array]])[, thisArg])Example:
let arr = [ 1 , 2 , 3 ] ;
let newArr = arr . map ( element => element * 2 ) ;
console . log ( newArr ) ; // Output: [2, 4, 6]
- **Definition:** Creates a new array with all elements that pass the test implemented by the provided function.
- **Syntax:** `array.filter(callback(element [, index [, array]])[, thisArg])`
- **Example:**
```javascript
let arr = [1, 2, 3, 4, 5];
let newArr = arr.filter(element => element % 2 === 0);
console.log(newArr); // Output: [2, 4]
```
Definition: Returns the value of the first element in the array that satisfies the provided testing function. Otherwise, it returns undefined.Syntax: array.find(callback(element [, index [, array]])[, thisArg])Example:
let arr = [ 5 , 12 , 8 , 130 , 44 ] ;
let found = arr . find ( element => element > 10 ) ;
console . log ( found ) ; // Output: 12
Definition: Returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1.Syntax: array.findIndex(callback(element [, index [, array]])[, thisArg])Example:
let arr = [ 5 , 12 , 8 , 130 , 44 ] ;
let foundIndex = arr . findIndex ( element => element > 10 ) ;
console . log ( foundIndex ) ; // Output: 1
Definition: Tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.Syntax: array.every(callback(element [, index [, array]])[, thisArg])Example:
let arr = [ 30 , 40 , 50 , 60 ] ;
let allOver20 = arr . every ( element => element > 20 ) ;
console . log ( allOver20 ) ; // Output: true
Definition: Tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value.Syntax: array.some(callback(element [, index [, array]])[, thisArg])Example:
let arr = [ 10 , 20 , 30 , 40 , 50 ] ;
let someOver30 = arr . some ( element => element > 30 ) ;
console . log ( someOver30 ) ; // Output: true
Definition: Determines whether an array includes a certain value among its entries, returning true or false as appropriate.Syntax: array.includes(valueToFind [, fromIndex])Example:
let arr = [ 1 , 2 , 3 ] ;
let includesTwo = arr . includes ( 2 ) ;
console . log ( includesTwo ) ; // Output: true
Definition: Returns the first index at which a given element can be found in the array, or -1 if it is not present.Syntax: array.indexOf(searchElement [, fromIndex])Example:
let arr = [ 2 , 9 , 9 ] ;
let index = arr . indexOf ( 9 ) ;
console . log ( index ) ; // Output: 1
Definition: Executes a reducer function on each element of the array, resulting in a single output value.Syntax: array.reduce(callback(accumulator, currentValue[, index, array])[, initialValue])Example:
let arr = [ 1 , 2 , 3 , 4 ] ;
let sum = arr . reduce ( ( acc , curr ) => acc + curr ) ;
console . log ( sum ) ; // Output: 10
Definition: Similar to reduce(), but applies the function from right to left instead of left to right.Syntax: array.reduceRight(callback(accumulator, currentValue[, index, array])[, initialValue])Example:
let arr = [ 'a' , 'b' , 'c' , 'd' ] ;
let concat = arr . reduceRight ( ( acc , curr ) => acc + curr ) ;
console . log ( concat ) ; // Output: 'dcba'
Definition: Creates and returns a new string by concatenating all of the elements in an array, separated by commas or a specified separator string.Syntax: array.join(separator)Example:
let arr = [ 'Hello' , 'World' ] ;
let str = arr . join ( ' ' ) ;
console . log ( str ) ; // Output: 'Hello World'
Definition: Reverses the elements of an array in place. The first array element becomes the last, and the last array element becomes the first.Syntax: array.reverse()Example:
let arr = [ 1 , 2 , 3 ] ;
arr . reverse ( ) ;
console . log ( arr ) ; // Output: [3, 2, 1]
Definition: Sorts the elements of an array in place and returns the sorted array.Syntax: array.sort([compareFunction])Example:
let arr = [ 5 , 2 , 1 , 4 , 3 ] ;
arr . sort ( ( a , b ) => a - b ) ;
console . log ( arr ) ; // Output: [1, 2, 3, 4, 5]
Definition: Returns a string representing the specified array and its elements.Syntax: array.toString()Example:
let arr = [ 1 , 2 , 3 ] ;
let str = arr . toString ( ) ;
console . log ( str ) ; // Output: '1,2,3'
Definition: Creates a new array with all sub-array elements concatenated into it recursively up to the specified depth.Syntax: array.flat([depth])Example:
let arr = [ 1 , 2 , [ 3 , 4 , [ 5 , 6 ] ] ] ;
let flatArr = arr . flat ( 2 ) ;
console . log ( flatArr ) ; // Output: [1, 2, 3, 4, 5, 6]
Definition: First maps each element using a mapping function, then flattens the result into a new array.Syntax: array.flatMap(callback(currentValue[, index[, array]])[, thisArg])Example:
let arr = [ 1 , 2 , 3 ] ;
let mappedArr = arr . flatMap ( x => [ x * 2 ] ) ;
console . log ( mappedArr ) ; // Output: [2, 4, 6]
Definition: Returns the number of elements in the array.Syntax: array.lengthExample:
let arr = [ 1 , 2 , 3 , 4 , 5 ] ;
console . log ( arr . length ) ; // Output: 5
Definition: Determines whether the passed value is an Array.Syntax: Array.isArray(value)Example:
let arr = [ 1 , 2 , 3 ] ;
console . log ( Array . isArray ( arr ) ) ; // Output: true
Definition: Fills all the elements of an array from a start index to an end index with a static value.Syntax: array.fill(value[, start[, end]])Example:
let arr = [ 1 , 2 , 3 , 4 , 5 ] ;
arr . fill ( 0 , 2 , 4 ) ;
console . log ( arr ) ; // Output: [1, 2, 0, 0, 5]
Definition: Returns a new Array Iterator object that contains the keys for each index in the array.Syntax: array.keys()Example:
let arr = [ 'a' , 'b' , 'c' ] ;
let iterator = arr . keys ( ) ;
for ( let key of iterator ) {
console . log ( key ) ; // Output: 0, 1, 2
}
Definition: Returns a new Array Iterator object that contains the values for each index in the array.Syntax: array.values()Example:
let arr = [ 'a' , 'b' , 'c' ] ;
let iterator = arr . values ( ) ;
for ( let value of iterator ) {
console . log ( value ) ; // Output: 'a', 'b', 'c'
}
Definition: Returns a new Array Iterator object that contains the key/value pairs for each index in the array.Syntax: array.entries()Example:
let arr = [ 'a' , 'b' , 'c' ] ;
let iterator = arr . entries ( ) ;
for ( let entry of iterator ) {
console . log ( entry ) ; // Output: [0, 'a'], [1, 'b'], [2, 'c']
}
Definition: Creates a new, shallow-copied Array instance from an array-like or iterable object.Syntax: Array.from(arrayLike[, mapFn[, thisArg]])Example:
let arrLike = 'hello' ;
let newArr = Array . from ( arrLike ) ;
console . log ( newArr ) ; // Output: ['h', 'e', 'l', 'l', 'o']
Definition: Copies a sequence of array elements within the array.Syntax: array.copyWithin(target, start[, end])Example:
let arr = [ 1 , 2 , 3 , 4 , 5 ] ;
arr . copyWithin ( 0 , 3 ) ;
console . log ( arr ) ; // Output: [4, 5, 3, 4, 5]
Definition: Returns the element at the specified index in the array.Syntax: array.at(index)Example:
let arr = [ 10 , 20 , 30 , 40 , 50 ] ;
console . log ( arr . at ( 2 ) ) ; // Output: 30
Definition: Returns the last index at which a given element can be found in the array, or -1 if it is not present. Searches the array from a specified index if provided.Syntax: array.lastIndexOf(searchElement[, fromIndex])Example:
let arr = [ 2 , 9 , 9 , 4 , 6 ] ;
let index = arr . lastIndexOf ( 9 ) ;
console . log ( index ) ; // Output: 2
Definition: Returns a string representing the elements of the array. The elements are converted to strings using their toLocaleString methods.Syntax: array.toLocaleString([locales[, options]])Example:
let arr = [ 1 , new Date ( ) , 'a' , { key : 'value' } ] ;
let str = arr . toLocaleString ( ) ;
console . log ( str ) ; // Output: '1,Sat Feb 27 2024 19:58:46 GMT+0000 (Coordinated Universal Time),a,[object Object]'
Definition: Creates a new Array instance with a variable number of arguments.Syntax: Array.of(element0[, element1[, ...[, elementN]]])Example:
let arr = Array . of ( 1 , 2 , 3 , 4 , 5 ) ;
console . log ( arr ) ; // Output: [1, 2, 3, 4, 5]
