页面禁用backspace键

<script type="text/javascript" language="javascript">

//全局禁用backspace键
document.onkeypress=check;
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.keyCode = 0;
        event.returnValue = false;
    }
    if(event.returnValue == undefined ){
        return true;
    }else{
        return event.returnValue;
    }
}

</script>