window.undefined is writable, use void(0)
The variable window.undefined is writable in a number of commonly used browsers. This can create confusion, but there is a simple way to get around it.
void(0) always returns the primitive value of undefined independently of what window.undefined is set to.
Note that this may affect the performance a bit since another function call has to be made. However, in most cases this can be neglected.
Written by Jesper Petersson
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3 Responses
You can also wrap your code in an IIFE and create a local undefined.
(function(window, undefined){
alert( typeof undefined ); // 'undefined'
}(window)),
@kevincennis yeah that's how jQuery does it!
I think is more readable just to compare undefined as string
typeof somevar === "undefined"
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