Question

I’ve created an array in JavaScript and inserted objects with keys of object_ids:

var ar = [];

ar[4] = 'a';
ar[2] = 'b';
ar[8] = 'c';
ar[5] = 'd';

Problem is when I print this out the array I get is:

[undefined, undefined, "b", undefined, "a", "d", undefined, undefined, "c"]

and

ar.length = 9

How do I prevent the array from auto filling with undefined values and simply save this array as a 4-element array?

Iteration over an array is not what I expect here.

Thanks!

Answer 1

Here’s what you are doing:

var ar = [];
ar[8] = 'c'; // creates [undefined, undefined, undefined, undefined, undefined, undefined, undefined, 'c'];

I believe this is what you want:

var ar = {};

ar[4] = 'a';
ar[2] = 'b';
ar[8] = 'c';
ar[5] = 'd';

Object.keys(ar).length == 4; // true

More information on Object.keys