How to initialize a hashmap of static values with integer keys in Javascript?

Question

Initializing a map having string keys can be performed as following in Javascript:

var xxx = {
    "aaa" : ["a1","a2","a3"],
    "bbb" : ["b1","b2","b3"],
    "ccc" : ["c1","c2","c3"],
    ...
};

I need to initialize some map with integer keys, something like:

var xxx = {
    0 : ["a1","a2","a3"],
    1 : ["b1","b2","b3"],
    2 : ["c1","c2","c3"],
    ...
};

Of course, I could proceed with an array like this:

xxx[0]=["a1","a2","a3"];
xxx[1]=["b1","b2","b3"];
xxx[2]=["c1","c2","c3"];
...

but the issue is that it makes the initialization code long. I need to squeeze all the bytes I can from it, because I need to push this object on the user side and any saved byte counts.

The xxx object needs to be initialized with n arrays, and each entry has a unique associated id between 0 and n-1. So, there is a one to one mapping between the id I can use and the arrays, and these ids are consecutive from 0 to n-1, which makes me think I could use an array instead of a Javascript 'map'.

I have noticed that one can push objects into an array. May be I could use something like this:

var xxx = [];
xxx.push(["a1","a2","a3"],["b1","b2","b3"],["c1","c2","c3"],...);

Is this a proper to achieve my objective or is there something smarter in Javascript? Thanks.

P.S.: Later, xxx will be referenced with something like xxx[2], xxx[10], etc...

Why don't you use var xxx = {0 : ["a1","a2","a3"], ...}, i.e. your second example? Number literals are valid property names in object literals. See es5.github.io/#x11.1.5. — Felix Kling
– Felix Kling, Commented Jul 30, 2013 at 11:02
Well I thought one could not use integers as map keys. May be I am wrong... — Jérôme Verstrynge
– Jérôme Verstrynge, Commented Jul 30, 2013 at 11:04
Well, you can ;) Every property name is converted to a string anyway. I.e. {0: 'foo'} is the same as {"0": 'foo'}. And after all, arrays are just objects too. The elements of an array are nothing but properties with numeric names. But maybe using an array would make more sense anyway. — Felix Kling
– Felix Kling, Commented Jul 30, 2013 at 11:04

Scott Sauyet · Accepted Answer · 2013-07-30 11:14:32Z

3

This strikes me as cleaner than using String or integer keys, though, unless you need to add additional properties on xxx:

var xxx = [
    ["a1","a2","a3"],
    ["b1","b2","b3"],
    ["c1","c2","c3"]
    //...
];

Just make xxx into an array containing arrays. You can get at, say, "b3", via xxx[1][2] (because xxx[1] == ["b1", "b2", "b3"].)

answered Jul 30, 2013 at 11:14

Scott Sauyet

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Jérôme Verstrynge Over a year ago

For the records, I have created a smalll jsfiddle to test the concept: jsfiddle.net/DVmHS

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