Create an array of given size in JavaScript

Creating an array of a given size can be implemented in many ways, and each way is useful in some conditions. We will explain each possible way to create an array with the given size with a proper example.

Below are the following ways:

Method 1: Using JavaScript array() constructor

In this method, we use the JavaScript Array constructor to create an array. It will just create an array without any value with a given size. However, the values of the array will be undefined.

Example: In this example, we are using an array constructor for the formation of an array.

Javascript

let arr = new Array(5);
console.log(arr.length);
console.log(arr)

Output

5
[ <5 empty items> ]

Method 2: Using apply() and map() Methods

We will use apply() and map() methods to create an array with the given size. It will create an array without any value with a given size. But the values of the array will be undefined.

Example 1: In this example, we are using the apply() and map() method for creating an array.

Javascript

let arr = Array.apply(null, Array(5))
    .map(function () { });

console.log(arr.length);
console.log(arr);

Output:

5
[undefined, undefined, undefined, undefined, undefined]

Example 2: We will put the values of the indexes so it will give you an array of length 5 and its values will be the index number 0, 1, 2, 3, 4.

Javascript

let arr = Array.apply(null, Array(5))
    .map(function (y, i) { return i; });

console.log(arr.length);
console.log(arr)

Output:

5
[0, 1, 2, 3, 4]

Method 3: Using JavaScript Array.from() Method

In ES6, we got something new called JavaScript Array.from() function, by which we can create an array of a given size.

Example: In this example, we are using Array.from() method for creating an array.

Javascript

let arr = Array.from(Array(5));
console.log(arr.length);
console.log(arr);

Output:

5
[undefined, undefined, undefined, undefined, undefined]

Example 2: In this example, we will pass the elements as arguments, each character will be an array element

Javascript

let arr = Array.from('GEEKSFORGEEKS');
console.log(arr.length);
console.log(arr)

Output:

13
["G", "E", "E", "K", "S", "F", "O", "R", "G", "E", "E", "K", "S"]

Example 3: In this example, we will pass a single element as a parameter and repeat the length we want in our array.

Javascript

let arr = Array.from('G'.repeat(5));
console.log(arr.length);
console.log(arr);

Output:

5
["G", "G", "G", "G", "G"]

Example 4: In this method, we will use two features of ES6, one JavaScript Array.from() function and the arrow function to create an array with a given size.

Javascript

let arr = Array.from({ length: 5 }, (x, i) => i);
console.log(arr.length);
console.log(arr)

Output:

5
[0, 1, 2, 3, 4]

Method 4: Using for loop

Looping in programming languages is a feature that facilitates the execution of a set of instructions repeatedly until some condition evaluates and becomes false.

Example: In this example, we are using for loop for creation of an array.

Javascript

const size = 5;
const array = [];

for (let i = 0; i < size; i++) {
  array.push(undefined);
}

console.log(array);

Output

[ undefined, undefined, undefined, undefined, undefined ]

To more about Arrays in JavaScript please go through Arrays in JavaScript