Using a variable as identifier in a json array

Question

Hi folks!

I'm wondering if it is possible to use assigned variables as identifier in a json array. When I tried this, I was getting some unexpected results:

(Code is simplified, parameters are passed in a different way)

var parameter = 'animal';
var value = 'pony';

Util.urlAppendParameters (url, {parameter : value});


Util.urlAppendParameters = function(url, parameters) {
    for (var x in parameters) {
        alert(x);
    }
}

Now the alert popup says: 'parameter' instead of 'animal'. I know I could use a different method (creating an array and assigning every parameter on a new line), but I want to keep my code compact.

So my question is: Is it possible to use a variable as an identifier in the json array, and if so, could you please tell me how?

Thanks in advance!

Answer 1

You will need to build your object in two steps, and use the [] property accessor:

var parameter = 'animal';
var value = 'pony';

var obj = {};
obj[parameter] = value;

Util.urlAppendParameters (url, obj);

I don't think JSON Array is the more correct term, I would call it Object literal.

Answer 2

Depending on your needs you could also build your object with a helper function;

Util.createParameters = function(args) {
    var O = {};
    for (var i = 0; i < arguments.length; i += 2)
        O[arguments[i]] = arguments[i + 1];
    return O
}

Util.urlAppendParameters (url, Util.createParameters(parameter, value, "p2", "v2"));

Answer 3

No, you can't use a variable as an identifier within an object literal like that. The parser is expecting a name there so you can't do much else but provide a string. Similarly you couldn't do something like this:

var parameter = 'animal';
var parameter = 'value'; //<- Parser expects a name, nothing more, so original parameter will not be used as name

The only work around if you really really want to use an object literal on a single line is to use eval:

Util.urlAppendParameters (url, eval("({" + parameter + " : value})");