javascript create empty array of a given size

1) To create new array which, you cannot iterate over, you can use array constructor:

Array(100) or new Array(100)


2) You can create new array, which can be iterated over like below:

a) All JavaScript versions

  • Array.apply: Array.apply(null, Array(100))

b) From ES6 JavaScript version

  • Destructuring operator: [...Array(100)]
  • Array.prototype.fill Array(100).fill(undefined)
  • Array.from Array.from({ length: 100 })

You can map over these arrays like below.

  • Array(4).fill(null).map((u, i) => i) [0, 1, 2, 3]

  • [...Array(4)].map((u, i) => i) [0, 1, 2, 3]

  • Array.apply(null, Array(4)).map((u, i) => i) [0, 1, 2, 3]

  • Array.from({ length: 4 }).map((u, i) => i) [0, 1, 2, 3]


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

We use Array.from({length: 500}) since 2017.


As of ES5 (when this answer was given):

If you want an empty array of undefined elements, you could simply do

var whatever = new Array(5);

this would give you

[undefined, undefined, undefined, undefined, undefined]

In newer versions, this now gives

[empty × 5]

See this other question on the difference between empty and undefined.

If you wanted it to be filled with empty strings, you could do

whatever.fill('');

which would give you

["", "", "", "", ""]

And if you want to do it in one line:

var whatever = Array(5).fill('');

Tags:

Javascript