Is it possible to overwrite the undefined in javascript?

Question

like

function myFunction(){
    var undefined = \"abc\";
}

If its possible then how to restrict not to allow that?

Answer 1

Some browsers allow it, the best way to restrict it is avoiding it.

But... some are using this technique to preserve the undefined:

(function(undefined){

})()

They get a variable called undefined but don't pass a value which gives undefined the undefined value.

From jQuery's source code:

(function( window, undefined ) {
    ...
    ...
})(window);