js 禁止F5刷新代码

<script language="JavaScript">
    window.onload = function() {
//禁止F5刷新
document.onkeydown = function (e) {
 if (e.keyCode === 116) {
   return false;
 }
};
//靜止右鍵
document.oncontextmenu = function() {event.returnValue = false;}
    }
</script>