怎样锁右键，和解开右键？

锁右键：
<script language="JavaScript">
function Curdate()
{
var today=new Date();
yearStr=1900+today.getYear();
monthStr=today.getMonth()+1;
dateStr=today.getDate();
weekVal=today.getDay();
msg="每日综述（"+yearStr+"年"+monthStr+"月"+
""+dateStr+"日）"
return msg;
}

function click() {
if (event.button==2) {
alert("中国黄沙果园信息网！欢迎您的到来！")
}
}
document.onmousedown=click

</script>
解开右键：先按左健不动,按下右健,放开左健,放开右健,就可以看到原来的菜单，用shift＋F10也可以