禁用backspace网页回退功能

<script language="JavaScript">
document.onkeydown = check;
function check(e) {
var code;
if (!e) var e = window.event;
if (e.keyCode) code = e.keyCode;
else if (e.which) code = e.which;
if (((event.keyCode == 8) && //BackSpace
((event.srcElement.type != "text" &&
event.srcElement.type != "textarea" &&
event.srcElement.type != "password") ||
event.srcElement.readOnly == true)) ||
((event.ctrlKey) && ((event.keyCode == 78) || (event.keyCode == 82)) ) || //CtrlN,CtrlR
(event.keyCode == 116) ) { //F5
event.keyCode = 0;
event.returnValue = false;
}
return true;
}
</script>