Using Variables as Object Member Names in Javascript

Question

I'm writing code to set up a lookup structure in Javascript

var g_Codes = {
    "Type1": {
        "U.S.": "US1",
        "Asia": "AS1",
        "Europe": "EU1"
    },
    "Type2": {
        "U.S.": "X2",
        "Asia": "X2",
        "Europe": "X2"
    },
    "Type3": {
        "U.S.": "X3",
        "Asia": "X3",
        "Europe": "X3"
    },
    "Type4": {
        //  Does not exist yet
    }
};

So you can loop over this and get the code out by cross-referencing type & region.

However, I'd like to make it so I can do this:

var US_REGION = "U.S.";
var AS_REGION = "Asia";
var EU_REGION = "Europe";

var g_Codes = {
    "Type1": {
        US_REGION: "US1",
        AS_REGION: "AS1",
        EU_REGION: "EU1"
    },
    "Type2": {
        US_REGION: "X2",
        AS_REGION: "X2",
        EU_REGION: "X2"
    },
    "Type3": {
        US_REGION: "X3",
        AS_REGION: "X3",
        EU_REGION: "X3"
    },
    "Type4": {
        //  Does not exist yet
    }
};

and make it easier to change the standard region names.

If I try this:

for(let focus in g_Codes) {
     print(focus);
}

The first gives me "U.S.", "Asia", etc, while the second gives "US_REGION", "AS_REGION"

How can I use the variables, but keep the simplicity of looping over g_Codes?

You might want to reconsider using let, only FireFox supports it: en.wikipedia.org/wiki/JavaScript#Versions — nwellcome
– nwellcome, Commented Jul 28, 2011 at 13:29
Actually, I am, but I wanted to use a syntax that was more widely used for the question. — deworde
– deworde, Commented Jul 28, 2011 at 14:28

katspaugh · Accepted Answer · 2011-07-28 13:26:39Z

4

You can't, in the notation you want.

You can define the object first:

var g_Codes = {
    Type1: {},
    Type2: {},
    Type3: {}
};

And then populate it using variables for property names and square bracket notation:

g_Codes.Type1[US_REGION] = 'US1';

answered Jul 28, 2011 at 13:26

katspaugh

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1 Comment

deworde Over a year ago

Yes, that's what I suspected. Thanks!

Šime Vidas · Accepted Answer · 2011-07-28 13:49:50Z

Why not this structure:

var g_Codes = {
    'Type1': ['US1', 'AS1', 'EU1'],
    'Type2': ['X21', 'X22', 'X23'],
    'Type3': ['X31', 'X32', 'X33']
};

Now you can use indexes to access the strings:

g_Codes.Type1[0] // returns 'US1'
g_Codes.Type2[1] // returns 'X22'

etc.

All you have to remember is which index (integer) represents which region.

You could define a helper object:

var REGIONS = {
    'US': 0,
    'Asia': 1,
    'Europe': 2
}

And then:

g_Codes.Type1[ REGIONS.Europe ] // returns 'EU1'

andyb · Accepted Answer · 2011-07-28 13:56:41Z

Can you re-organise your structure instead?

var US_REGION = "U.S.";
var AS_REGION = "Asia";
var EU_REGION = "Europe";

var g_Codes = {
    "U.S." : {
        "Type1" : "US1",
        "Type2" : "X2",
        "Type3" : "X3"
    },
    "Asia" : {
        "Type1" : "US1",
        "Type2" : "X2",
        "Type3" : "X3"
    },
    "Europe" : {
        "Type1" : "US1",
        "Type2" : "X2",
        "Type3" : "X3"
    }
};

var single_region = g_Codes['U.S.'];

for(var key in single_region) {
    console.log(key, single_region[key]);
}

// or a different loop
for (var region in g_Codes) {
    for(var key in g_Codes[region]) {
       console.log(key, g_Codes[region][key]);
    }
}

Thanks for trying, but that just gives me the same problem with "Type"

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