How do I efficiently create multi-dimensional javascript array?

Question

I need to store information similar to this:

tag_array['design1']['0'][0]['x'] = 100;
tag_array['design1']['0'][0]['y'] = 100;
tag_array['design1']['0'][0]['w'] = 710;
tag_array['design1']['0'][0]['h'] = 332;

This would work if it is PHP but it's not working in javascript.

How do I create the same array in proper javascript syntax?

well you would be better off with objects than arrays since you are using strings. — epascarello
– epascarello, Commented Sep 5, 2012 at 18:23

gen_Eric · Accepted Answer · 2012-09-05 18:49:46Z

2

In PHP, you can do that because it will make the parent elements too (it actually throws a warning). In JavaScript, it will error out because the parent elements don't exist.

Instead of making it like that, try to make it all at once like this:

var tag_array = {
    design1: {
        '0': [{
            x: 100,
            y: 100,
            w: 710,
            h: 332
        }]
    }
};

This should give you the structure you want.

UPDATE: Answer has been updated to reflect the fact that the 1st 0 can be a string.

edited Sep 5, 2012 at 18:49

answered Sep 5, 2012 at 18:24

gen_Eric

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6 Comments

epascarello Over a year ago

but it is a string "0" not an integer.

Pointy Over a year ago

String versions of numeric properties can be used with numerically-indexed array elements, @epascarello, but you're right it's not clear which setup the OP wants.

JC Lee Over a year ago

OP here. Yes, the first "0" is a string. Can be replaced with any other strings.

benekastah Over a year ago

In javascript, when you access a property it is accessed as a string. Since arrays are just fancy objects, they behave the same way. a[0] and a["0"] do the same thing because in the first case the number 0 is converted to a string before looking up the property.

JC Lee Over a year ago

@Rocket How do I directly insert into number 4 using your syntax? Like the following: tag_array['design1']['0'][4]

|

Paul S. · Accepted Answer · 2012-09-05 19:53:54Z

-1

If you want to do it programatically then because JavaScript requires you to have this type of structure

tag_array = {};
tag_array['design1'] = {};
tag_array['design1']['0'] = [];
tag_array['design1']['0'][0] = {};
tag_array['design1']['0'][0]['x'] = 100;

you can make a prototype function to create the object/array structure for you

Object.defineProperty(Object.prototype, 'addDimensions', { value: function(){
    var prop = arguments[0];
    if(this[prop] !== undefined){
        if(typeof this[prop] !== 'object') throw 'Property "'+prop+'" is already defined.'
    }else{
        if(arguments.length > 1 && ~~arguments[1] === arguments[1] && arguments[1] >= 0) this[prop] = [];
        else this[prop] = {};
    }
    if(arguments.length > 1){
        this[arguments[0]].addDimensions.apply(
            this[arguments[0]],
            Array.prototype.slice.call(arguments,1)
        );
    }
    return this;
},
enumerable: false });

and call it on an empty object {}

var myArrayLikeObject = ({}).addDimensions('design1','0',0); // {design1: [ [ {} ] ] }

or an array [] (only if first arg is an integer)

var myMultiArray = [].addDimensions(0,'hi',0); // [ {hi: [ {} ] } ]

or on an existing array or object

var a = [0,1,2];
a.addDimensions(3,0); // a = [0, 1, 2, [ {} ] ]

edited Sep 5, 2012 at 19:53

answered Sep 5, 2012 at 18:56

Paul S.

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3 Comments

Paul S. Over a year ago

You'll need to modify it a little to check for existing sub-arrays / objects if you want to call it multiple times on the same indices

Bergi Over a year ago

-1: a) Never add enumerable properties to Object.prototype, b) use objects ({}) for non-numeric properties, not arrays

Paul S. Over a year ago

@Bergi, does the edit I just made solve the issues you had with it?

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