How can I know if a window cannot scroll anymore to the right?

I have a scrolling function over a recursive TimeOut making a very width window 开发者_运维百科scroll horizontally until it reaches the right end, but I need to know in JavaScript if the scrolling has finished to change the direction and scroll back to the origin.

How can I accomplish this?

function ScrollIt(scrollPos, direction) {
  if(direction == 'right')
   window.scrollBy(scrollPos,0);
  else
   window.scrollBy(scrollPos,0);
  cTimeOut = setTimeout("ScrollIt(1,'right')",10);
}

Of course I call the function in the onload event the first time.

Thanks in advance.

---

var w = document.documentElement.clientWidth;
var over = document.documentElement.scrollWidth - w;

window.onscroll = function() {
  // Detect webkit browser (Chrome, Safari)
  if(window.devicePixelRatio) {
    if(document.body.scrollLeft==over) { alert("KABOOM (Webkit)") }
  }
  else {
    if(document.documentElement.scrollLeft == over) { alert("CRUNCH") }
  }
}

Tested FF 3.6, IE8, Chrome 3.1, Safari 4.0