Javascript: "undefined" == undefined ??

Question

var a;
var b = "undefined";
alert(typeof a == b);
// true

Could anyone explain me why is it true? For my understanding, a is an undefined variable and b is a string with an existing value that happens to be "undefined".

Answer 1

A typeof always returns a string, that's the reason why typeof a == b(when b is assigned a string value "undefined") is true.
And also "undefined" != undefined. "undefined" == string, while undefined == special data type.

Answer 2

Infinite Thanks! That was the missing puzzle :)

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof