javascript禁止网页右键的方法

<script type="text/javascript">
/**
 禁止右键菜单
site www.jb200.com
*/
  function block(oEvent){
   if(window.event)
    oEvent=window.event;
   if(oEvent.button==2)
    alert("鼠标右键不可用");
  }
  document.onmousedown=block;
</script>

<script language="JavaScript">
<!--
if (window.Event) 
document.captureEvents(Event.MOUSEUP); 
function nocontextmenu() {
event.cancelBubble = true
event.returnValue = false;
return false;
}
function norightclick(e) {
if (window.Event){
   if (e.which == 2 || e.which == 3)
   return false;
}else{
   if (event.button == 2 || event.button == 3){
       event.cancelBubble = true
    event.returnValue = false;
       return false;
    }
}
}
document.oncontextmenu = nocontextmenu; // for IE5+
document.onmousedown = norightclick; // for all others
//-->
</script>