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Is this Javascript object literal key restriction strictly due to parsing?

Asked 2010-05-20T11:21:20.497
10

Please refer to the code below, when I "comment in" either of the commented out lines, it causes the error (in IE) of "':' expected". So then is my conclusion correct, that this inability to provide a reference to an object value, as an object key in a string literal; is this strictly an interpreter/parsing issue? Is this a candidate for an awful (or at least "bad") "part" of Javascript, in contrast to Crockford's "good parts"?

<script>
var keys = {'ONE': 'one'};

//causes error:
//var obj1 = {keys.ONE: 'value1'};
//var obj1 = {keys['ONE']: 'value1'};

//works
var obj1 = {};
obj1[keys.ONE] = 'value1';

//also works
var key_one = keys.ONE;
var obj2 = {key_one: 'value1'};
</script>
javascript object parsing object-literal
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2 Answers

15

The limitation of the literal object syntax is that the names has to be literal. As the names can be specified as an identifer as well as a string, it's not possible to use a variable instead.

This will create an object with a property n, not a property answer:

var n = 'answer';
var o = { n: 42 };
answered 2010-05-20T11:28:47.407
1

You can try:

var obj = {};
var val = 'foo';

obj[val] = 'bar'; 

obj.foo >>> 'bar';
answered 2012-08-14T15:29:17.773

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