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('');