Does JavaScript array.forEach traverse elements in ascending order

Question

In JavaScript I can have an array with holes:

a = [];
a[0] = 100;
a[5] = 200;
a[3] = 300;

a.forEach(function(x) {alert(x);});

I could not

Answer 1

Straight out of the ECMAScript standard

forEach calls callbackfn once for each element present in the array, in ascending order. callbackfn is called only for elements of the array which actually exist; it is not called for missing elements of the array.

So Array.forEach will skip certain elements in an array. Your example

a.forEach( function( value ) { console.log( value ) }); // prints 100, 300, 200

If you do want to traverse the array in ascending order and all your elements are numbers then you can sort the array beforehand like so

a.sort( function( a, b ) { return a - b });
// this now prints 100, 200, 300
a.forEach( function( value ) { console.log( value ) });