javascript - TypeOf undefined instead of comparing against undefined? -

in javascript, why people write typeof myvar == "undefined" instead of myvar == undefined?

is compatibility reasons?

this main reason:

if(a == undefined) console.log('test') >> referenceerror: not defined if(typeof == "undefined") console.log('test') >> test 

but if run comparison:

if(window.a == undefined) console.log('test') >> test 

so if use a standalone variable can't. using window it's possible, , doesn't matter approach use, stated in comment it's safer use typeof not every variable belongs window scope.