Javascript | Set all values of an array

Question

Code

var cool = new Array(3); cool[setAll] = 42; //cool[setAll] is just a pseudo selector.. alert(cool); 

Result

A alert message:

42,42,42 

How do I change/set all values of an array to a specific value?

Answer 1

There's no built-in way, you'll have to loop over all of them:

function setAll(a, v) {     var i, n = a.length;     for (i = 0; i < n; ++i) {         a[i] = v;     } } 

http://jsfiddle.net/alnitak/xG88A/

If you really want, do this:

Array.prototype.setAll = function(v) {     var i, n = this.length;     for (i = 0; i < n; ++i) {         this[i] = v;     } }; 

and then you could actually do cool.setAll(42) (see http://jsfiddle.net/alnitak/ee3hb/).

Some people frown upon extending the prototype of built-in types, though.

EDIT ES5 introduced a way to safely extend both Object.prototype and Array.prototype without breaking for ... in ... enumeration:

Object.defineProperty(Array.prototype, 'setAll', {     value: function(v) {         ...     } }); 

EDIT 2 In ES6 draft there's also now Array.prototype.fill, usage cool.fill(42)