Best-Known JavaScript Array Methods

An array is a special variable in all programming languages used to store multiple elements. JavaScript array come with built-in methods that every developer should know how to use. These methods help in adding, removing, iterating, or manipulating data as per requirements.

There are some Basic JavaScript array methods which are as follows:

Array some() Method

The Array some() method checks if at least one element of the array satisfies the condition implemented by the provided function.

Example: To demonstrate the use of the Array some() method.

// JavaScript to illustrate
// lastIndexOf() method
function isGreaterThan5(element, index, array) {
    return element > 5;
}

function func() {
    // Original array
    let array = [2, 5, 8, 1, 4];

    // Checking for condition in array
    let value = array.some(isGreaterThan5);

    console.log(value);
}

func();

true

Array reduce() Method

The array reduce() method reduces an array to a single value by executing a provided function for each value from left to right.

Example: Use the reduce() method to accumulate values, such as subtracting numbers.

// Original array
let numbers = [88, 50, 25, 10];

// Performing reduce method
let sub = numbers.reduce(geeks);

function geeks(total, num) {
    return total - num;
}

console.log(sub);

3

Array map() Method

The map() method in JavaScript creates a new array by calling a specific function on each element of the parent array. It does not mutate the original array.

Example: To demonstrate the use of the Array map() method.

// Original array
let numbers = [4, 9, 16, 25];

// Performing map method
let sub = numbers.map(geeks);

function geeks() {
    return numbers.map(Math.sqrt);
}

console.log(sub);

[ [ 2, 3, 4, 5 ], [ 2, 3, 4, 5 ], [ 2, 3, 4, 5 ], [ 2, 3, 4, 5 ] ]

Array every() Method

The Array every() method checks if all elements in the array satisfy a given condition provided by a function.

Example: To demonstrate the use of the Array every() method.

// JavaScript code for every() function
function ispositive(element, index, array) {
    return element > 0;
}

function func() {
    let arr = [11, 89, 23, 7, 98];

    // Check for positive number
    let value = arr.every(ispositive);

    console.log(value);
}

func();

true

Array flat() Method

The Array flat() method creates a new array that contains more than arrays. Basically creates a simple array from an array that contains multiple arrays.

Example: To demonstrate the use of the Array flat() method.

//Original array
let arr = [[11, 89], [23, 7], 98];

// Performing flat method
let geeks = arr.flat();

console.log(geeks);

[ 11, 89, 23, 7, 98 ]

Array flatMap() Method

This Array flatMap() method is used to flatten the input array element into a new array. This method first of all map every element with the help of a mapping function, then flattens the input array element into a new array.

Example: To demonstrate the use of the Array flatMap() method.

const myAwesomeArray = [
    [1], [2], [3], [4], [5]
];

let geeks = myAwesomeArray.flatMap(
    (arr) => arr * 10
);
console.log(geeks);

[ 10, 20, 30, 40, 50 ]

Array filter() Method

The Array filter() method is used to create a new array from a given array consisting of only those elements from the given array which satisfy a condition set by the argument function.

Example: To demonstrate the use of the Array filter() Method.

function isPositive(value) {
    return value > 0;
}

function func() {
    let filtered = [112, 52, 0, -1, 944]
    .filter(isPositive);
    console.log(filtered);
}

func();

[ 112, 52, 944 ]

Array findindex() Method

The Array findIndex() method returns the index of the first element in a given array that satisfies the provided testing function. Otherwise, -1 is returned.

Example: To demonstrate the use of the Array.findindex() method.

let array = [10, 20, 30, 110, 60];

function finding_index(element) {
    return element > 25;
}

console.log(array
    .findIndex(finding_index)
);

2

Array find() Method

The Array find() method is used to get the value of the first element in the array that satisfies the provided condition. It checks all the elements of the array and whichever the first element satisfies the condition is going to print.

Example: To demonstrate the use of the Array find() method.

// Input array contain some elements.
let array = [10, 20, 30, 40, 50];

// Function (return element > 10).
let found = array.find(function (element) {
    return element > 20;
});

// Printing desired values.
console.log(found);

30

Array fill() Method

The Array fill() method is used to fill the array with a given static value. The value can be used to fill the entire array or it can be used to fill a part of the array.

Example: To demonstrate the use of the Array fill() Method.

// JavaScript code for fill() function
let arr = [1, 23, 46, 58];

// Here value = 87, start index = 1 and
// and last index = 3
arr.fill(87, 1, 3);
console.log(arr);

[ 1, 87, 87, 58 ]

Array forEach() Method

The Array forEach() method calls the provided function once for each element of the array. The provided function may perform any kind of operation on the elements of the given array.

Example: To demonstrate the use of the Array forEach() Method.

// Original array
const items = [1, 29, 47];
const copy = [];

items.forEach(function (item) {
    copy.push(item * item);
});

console.log(copy);

[ 1, 841, 2209 ]

Array sort() Method

The Array sort() method is used to sort the array. An array can be of any type i.e. string, numbers, characters, etc.

Example: To demonstrate the use of the Array sort() Method.

// Original array
let numbers = [88, 50, 25, 10];

// Performing sort method
let sub = numbers.sort(geeks);

function geeks(a, b) {
    return a - b;
}

console.log(sub);

[ 10, 25, 50, 88 ]

Array concat() Method

The Array concat() method is used to merge two or more arrays together. This function does not alter the original arrays passed as arguments.

Example: To demonstrate the use of the Array concat() Method.

// JavaScript code for concat() function
let num1 = [11, 12, 13],
    num2 = [14, 15, 16],
    num3 = [17, 18, 19];

console.log(num1.concat(num2, num3));

[
  11, 12, 13, 14, 15,
  16, 17, 18, 19
]

Array includes() Method

The Array includes() method is used to know whether a particular element is present in the array or not and accordingly, it returns true or false i.e, if the element is present, then it returns true otherwise false

Example: To demonstrate the use of the Array includes() Method.

// Taking input as an array A
// having some elements.
let A = [1, 2, 3, 4, 5];

// Include() function is called to
// test whether the searching element
// is present in given array or not.
let a = A.includes(2);

// Printing result of function.
console.log(a);

true

Array reverse() Method

The Array reverse() method is used for in-place reversal of the array. The first element of the array becomes the last element and vice versa.

Example: To demonstrate the use of the Array reverse() method.

//Original Array
let arr = [34, 234, 567, 4];
console.log("Original array: " + arr);

//Reversed array
let new_arr = arr.reverse();

// Display the result
console.log("Newly reversed array: " + new_arr);

Original array: 34,234,567,4
Newly reversed array: 4,567,234,34