Here, the output is 9, however I don't see anything related to 9 or how it could give an output of 9. How is it possible??

Question

var x = 6;
var y = 0;
while(x>0 && y<6) {
x--;
y += x;
}
document.write(y);

Answer 1

If we run through the loop, it's easier to understand.
x = 6
y = 0
x-- //x = 5
y += x // y = 5
/*next iteration*/
x-- // x = 4
y += x // y = 9
y is bigger than 6, so the loop stops there

Answer 2

Thanks so much Airree for that vivid explanation

Answer 3

not understand