How to create a zero filled JavaScript array of arbitrary length? [duplicate]

In Javascript ES6 there is a very easy solution. I came here because I'm trying to codegolf it shorter:

n = 999  // arbitrary length
a = Array(n).fill(0)

console.log(a)

By default Uint8Array, Uint16Array and Uint32Array classes keep zeros as it's values, so you don't need any complex filling techniques, just:

var ary = new Uint8Array(10); 

all elements of array ary will be zeros by default.

New ES6 array extensions allow you to do this natively with fill method. Now IE edge, Chrome and FF supports it, but check the compatibility table

new Array(3).fill(0) will give you [0, 0, 0]. You can fill the array with any value like new Array(5).fill('abc') (even objects and other arrays).

On top of that you can modify previous arrays with fill:

arr = [1, 2, 3, 4, 5, 6]
arr.fill(9, 3, 5)  # what to fill, start, end

which gives you: [1, 2, 3, 9, 9, 6]

If you want a 9-length array:

Array.apply(null, {length: 9}).map(function() {return 0;})

If you want a X-length array:

Array.apply(null, {length: X}).map(function() {return 0;})

If you have an array and want to rewrite its values:

var arr=[54,53,6,7,88,76]
arr=arr.map(function() {return 0;})

You can fill the array with anything you want, just by changing the value at return inside the function inside .map:

Array.apply(null, {length: 9}).map(function() {return "a string";})
Array.apply(null, {length: 9}).map(function() {return Math.random();})
Array.apply(null, {length: 9}).map(function() {return NaN;})
Array.apply(null, {length: 9}).map(function() {return null;})
Array.apply(null, {length: 9}).map(function() {return true;})
Array.apply(null, {length: 9}).map(function() {return;})

The last one will fill the array with undefined

function repeatArray(value, len){
  var A=[],i=0;
  while (i<len) A[i++]= value;
  return A;
}

I tested both the Unit8Array

[].slice.apply(new Uint8Array(n));

and the join/split method

new Array(n + 1).join('0').split('').map(parseFloat);

in jsPerf with interesting results. Chrome and Firefox were fairly slow on both counts (between 48,000 and 76,000 operations). But Opera and Safari both did amazingly well with the Uint8Array function (up to 438,000 operations). I think I'll start using Uint8Array and hope Chrome and Firefox improve.

One way could use recursion.

function fillArray(l, a) {
  a = a || [];
  if (0 < l) {
    l -= 1;
    a[l] = 0;
    return fillArray(l, a);
  }
  return a;
}

I had also posted a more classic option:

function fillArray(l) {
  var a;
  for (a = []; 0 < l; l-=1, a[l]=0);
  return a;
}