关于Javascript速记对象引用的问题

Question

I'm pretty new to javascript and am wondering about quoting the keys in object shorthand

So I am using the OpenLayers js library and many of the object constructors take {options} as the argument for setting different variables, callbacks, etc.

In my code I have a bunch of control objects which are used to manipulate the map and what-not

    controls = {
        navigation   : new OpenLayers.Control.Navigation({'autoActivate' : false}),
        zoom_out_box : new OpenLayers.Control.ZoomBox({
            alwaysZoom  : true,
            out         : true
        }),
        ...     
    };

In some of their examples they use single quotes for the keys and others they won't {'ascending':false} or {visibility: false} .

I thought that maybe it had to do with reserved words or functions vs variables but I can add functions to my zoom box:

controls= {
        zoom_out_box : new OpenLayers.Control.ZoomBox({
            if      : function(e){alert('blah');}
        }),
       zoom_out_box_2 : new OpenLayers.Control.ZoomBox({
            'if'    : function(e){alert('blah');}
        })
};

I test it with an onlclick="controls.zoom_out_box.if(this)" and it alerts fine and I get no warnings or errors in firebug.

So whats the difference in the quoting?

Answer 1

You can use non-identifiers as keys in a JavaScript object, in which case, the quotes are required:

var obj = { 'not-an-identifier': 42 };

In the case where an identifier is quoted, it's just a matter of style/preference/convention.

As a side note, non-identifiers must always be accessed using the square-bracket/array-style notation ( obj['not-an-identifier'] ), rather than the dot ( . ) notation.

Answer 2

The currently accepted answer is incorrect:

You can use non-identifiers as keys in a JavaScript object, in which case, the quotes are required

The quotes aren't required if you use a numeric literal as a property name.

From Unquoted property names / object keys in JavaScript , my write-up on the subject:

Quotes can only be omitted if the property name is a numeric literal or a valid identifier name .

[…]

Bracket notation can safely be used for all property names.

[…]

Dot notation can only be used when the property name is a valid identifier name.

I also made a tool that will tell you if any given property name can be used without quotes and/or with dot notation. Try it at mothereff.in/js-properties .