While and postfix/prefix

Question

var a = 20;
var b = 0;
a = --a;
while(a>a--){
b++;
}
document.write(b);

//outputs 0. I don't understand lines 3-5. Can anyone help? Thank you

Answer 1

Line 3 decrements a. Line 4 is "while a is greater than a"; then it decrements a (post, not pre) So it will find that a !> a, so b won't be incremented. Therefore b stays at 0 and then is printed.

Answer 2

very helpful thank you