Javascript array alllocation

Question

I was dealing with a problem and got to the point where I thought I could use the Ids to my entity instances as array indices for easy lookup.

var myArray = [];
myArray[obj.Id] = true;

Assume obj.Id is 1000 here, so will be myArray.length. Am I allocating 1000 bytes for a single boolean value here or is it just returning the maximum index as length?

Why not use a key value style object, `var myArray = {}; myArray[obj.Id] = true;` — Arun P Johny, Mar 29 '16 at 05:08
it's "_returning the maximum index as length_", but sparse arrays slow down `[].map()` and `for(i=0;i — dandavis, Mar 29 '16 at 05:16

score 2 · Accepted Answer · answered Mar 29 '16 at 05:11

2

It won't be allocating so many bytes.

But what you are really looking for is an key-value object like

var myObj = {};
myObj[obj.Id] = true;
//then to access
console.log(myObj[obj.Id])

answered Mar 29 '16 at 05:11

Arun P Johny

384,651
66
527
531

Thanks. Yes I did use the object approach eventually. I was just interested to know if array space allocation is based on index. – Vahid Mar 29 '16 at 05:14
And could you please explain why is using objects rather than array is a better approach then? – Vahid Mar 29 '16 at 05:18

Javascript array alllocation

1 Answers1