Question

I’m trying to work out what is considered valid for the property name of a javascript object. For example

var b = {}
b['-^colour'] = "blue";     // Works fine in Firefox, Chrome, Safari
b['colour'] = "green";      // Ditto
alert(b['-^colour']);       // Ditto
alert(b.colour);            // Ditto
for(prop in b) alert(prop); // Ditto
//alert(b.-^colour);     // Fails (expected)

This post details valid javascript variable names, and ‘-^colour’ is clearly not valid (as a variable name). Does the same apply to object property names? Looking at the above I’m trying to work out if

1. b[‘-^colour’] is invalid, but works in all browsers by quirk, and I shouldn’t trust it to work going forward

2. b[‘-^colour’] is completely valid, but it’s just of a form that can only be accessed in this manner – (it’s supported so Objects can be used as maps perhaps?)

3. Something else

As an aside, a global variable in javascript might be declared at the top level as

var abc = 0;

but could also be created (as I understand it) with

window['abc'] = 0;

the following works in all the above browsers

window['@£$%'] = "bling!";
alert(window['@£$%']);

Is this valid? It seems to contradict the variable naming rules – or am I not declaring a variable there? What’s the difference between a variable and an object property name?

Answer 1

Yes, objects can be used as maps, and any string can be a property name. As you’ve discovered, some properties can only be accessed using the bracket syntax.

window['abc']

is accessing a property. It is not a variable, even though it refers to the same value (at the global level) as:

abc