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Recipe · Arrays

How to Create Arrays with a Specific Length in JavaScript

Published 23 Jun 20233 methods

Quick answer

Using the Array() constructor
let arr = new Array(5);

Other methods on this page: Using the Array.of() method, Using the Array.from() method

Using the Array() constructor

In JavaScript, you can create arrays of a specific length using the Array() constructor, which creates a new Array object with a specified number of undefined items. An example of how to create an array of length 5 is given below:


let arr = new Array(5);

How it works

The ‘new Array()’ constructor in JavaScript creates an empty array with a length property set to the number of arguments provided during array creation. In our example, we’ve specified ‘5’ as the argument to create an array of length 5.

  • Firstly, the ‘new’ keyword is used to create a new instance of an object. In our case, we’re creating a new instance of the Array object.
  • Next, we call the Array() constructor. A constructor is a special method that’s used to initialize a newly created object. For the Array object, it accepts a number as an argument representing the desired length of the array.
  • We provide ‘5’ as an argument to the Array() constructor, specifying that we want to create an array of length 5.
  • Finally, the newly created array ‘arr’ has a length of 5, but contains no values – it is an array of 5 empty slots.

Using the Array.of() method

The Array.of() method in JavaScript creates a new Array instance with a variable number of arguments, regardless of number or type of the arguments. It’s a better way to create arrays with a single element or multiple elements. You can understand it better with the example given below:


let array1 = Array.of(5);
let array2 = Array.of('5');
let array3 = Array.of(1,2,3,4,5);

How it works

The Array.of() method creates a new Array instance from a variable number of arguments, regardless of the number or type. In the case of passing a single argument, the method will still create an array with a single item, unlike the Array() constructor that would interpret the argument as the length of the array.

  1. Array.of(5): Here, 5 is not the size of the array, but the first and only element. So, array1 will be [5].
  2. Array.of(‘5’): Here, ‘5’ is not the size of the array, but the first and only element. So, array2 will be [‘5’].
  3. Array.of(1,2,3,4,5): This creates an array with elements 1,2,3,4,5. So, array3 will be [1,2,3,4,5].

Using the Array.from() method

The Array.from() method in JavaScript creates a new array instance from an iterable or array-like object, which we can utilize to create arrays of a specific length. It is more clear when we explore this through an example:


let arrayLength = 5;
let newArray = Array.from({length: arrayLength}, (v, i) => i);

How it works

The Array.from() method takes two arguments: the array-like or iterable object to convert to an array and a map function to call on every element of the array.

  • First, we define a variable arrayLength to specify the desired length of the array.
  • We then call Array.from() method and pass an object with a property of length which is set to the desired array length.
  • The second argument to Array.from() is a map function, which is called on every element of the array. In this case, it’s an arrow function (v, i) => i, which simply returns the index, i, for each element.
  • As a result, newArray will be an array of increasing numbers from 0 to arrayLength - 1.