文字左右滚动效果

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>为什么受伤的总是我</title>
<script language="javascript" type="text/javascript">
var dir = "left";
function sroll(){
var title = document.title;
if(dir=="left"){
   var first = title.charAt(0);
   var last = title.substring(1,title.length);
   document.title = last+first;
  }
  else{
   title.re
   var first = title.charAt(title.length-1);
   var last = title.substring(0,title.length-1)
   document.title = first+last;
  }

}
setInterval("sroll()",500);
function GoLeft(){
  dir = "left";
}
function GoRight(){
  dir="right";
}
</script>
</head>