Why doesnt this work?

Question

I'm trying to make it give an alert if you clicked within the given x and y but it desn't work, why?
c.addEventListener('click', function(evt){
if(
evt.X > headX &&
evt.X < headX += headW &&
evt.Y > headY &&
evt.Y < headY += headH
)
alert('You clicked it');
});

Answer 1

Why +=
Why not just +
Like "headX + headW"

Answer 2

Yea I figured it out a little while ago but thanks