javascript屏蔽F5刷新键

<script language="Javascript">
function KeyDown(){
//alert(event.keyCode);
  if ((event.keyCode==116)|| //屏蔽 F5 刷新键
(event.ctrlKey && event.keyCode==82)){ //Ctrl + R
event.keyCode=0;
event.returnValue=false;
}

}
document.onkeydown=KeyDown;
</script>