How to initialize an array in JavaScript ?

Initializing an array in JavaScript involves creating a variable and assigning it an array literal. The array items are enclosed in square bracket with comma-separated elements. These elements can be of any data type and can be omitted for an empty array.

Initialize an Array using Array Literal

Initializing an array using the array literal involves directly assigning square brackets [] to a variable. It creates an empty array or populates it with elements enclosed within the brackets.

Example: Create an array using array literal.

const arr1 = [];

console.log("Empty Array: ", arr1);

const arr2 = [10, 20, 30, 40, 50];

console.log("Array with Items: ", arr2);

Empty Array:  []
Array with Items:  [ 10, 20, 30, 40, 50 ]

Example 2: Line breaks and new lines do not impact arrays, they store in their normal way.

const arr = [
10,
20,
30,
40,
50
];

console.log("Array Elements: ", arr);

Array Elements:  [ 10, 20, 30, 40, 50 ]

Other options to initialize an array in JavaScript are listed below:

Using Array() Constructor

Initializing an array using Array constructor involves invoking new Array() and optionally passing initial elements as arguments. Alternatively, specifying the desired length as a single argument creates an array with undefined elements.

Example: Creating and initializing an array using array() constructor. It creates an array as an object.

// Create an empty array
const arr1 = new Array();
console.log("Empty Array", arr1);

// Create and Initialize an array
const arr2 = new Array(10, 20, 30, 40, 50);
console.log("Array Elements: ", arr2);

// Create an Array of Given size
const arr3 = new Array(5);
console.log("Array of size 5: ", arr3);

Empty Array []
Array Elements:  [ 10, 20, 30, 40, 50 ]
Array of size 5:  [ <5 empty items> ]

Using Array.of() Method

The Array.of() method in JavaScript creates a new array instance with a variable number of elements. This method ensures the exact elements are added to the array, avoiding unexpected behaviors with other array creation methods like Array() constructor.

Example: Initializing an array using array.of() method.

let arr = Array.of(1, 2, 3, 4);
console.log("Array Elements: ", arr);

Array Elements:  [ 1, 2, 3, 4 ]

Using Array.from() Method

The Array.from() method creates an array from iterable objects. It takes two arguments: an object with a length property and a map function. The map function can be used to initialize elements.

Example: Creating an array of length 5 using Array.from() with values incrementing from 1 to 5.

const arr = Array.from({ length: 5 }, (_, i) => i + 1);
console.log(arr);

[ 1, 2, 3, 4, 5 ]

Difference Between Array() Constructor and Array Literal []