what is the"px"?why the pos>=150not =150?

Question

window.onload = function() {
var pos = 0;
//our box element
var box = document.getElementById('box');
var t = setInterval(move, 10);

function move() {
if(pos >= 150) {
clearInterval(t);
}
else {
pos += 1;
box.style.left = pos+'px';
}
}
};

Answer 1

px is unit pixels;
>= is safer. but if you move only with pos+=1 you can check (pos=150) too

Answer 2

but when i change pos>=150to=150,it does'nt work

Answer 3

liu Mr.
It's supposed to be == for comparison not = since = is assignment

Answer 4

Thank you all!My question is solved!