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>