Benefit of using 'window' prefix in javascript

Question

Are there any benefits to using the 'window' prefix when calling javascript variables or methods in the window object? For example, would calling 'window.alert' have an advantage over simply calling 'alert'? I can imagine using the prefix could give a small performance boost when the call is made from inside some function/object, however I rarely see this in people's code. Henceforth this question.

Answer 1

This is useful when attempting to test global object values. For example, if GlobalObject is not defined then this throws an error:

if(GlobalObject) { // <- error on this line if not defined
    var obj = new GlobalObject();
}

but this does not throw an error:

if(window.GlobalObject) { // Yay! No error!
    var obj = new GlobalObject();
}

Similarly with:

if(globalValue == 'something') // <- error on this line if not defined
if(window.globalValue == 'something') // Hurrah!

and:

if(globalObj instanceof SomeObject) // <- error on this line if not defined
if(window.globalObj instanceof SomeObject) // Yippee! window.prop FTW!

I would not expect to see a significant performance difference, and the only other reason you might do this is to ensure that you are actually getting a value from the global scope (in case the value has been redefined in the current scope).