网页用JS屏蔽各种按键代码

<script>
    //屏蔽鼠标右键Ctrl+N、Shift+F10、F11、F5刷新、退格键
    function document.oncontextmenu(){ event.returnValue = false; }
    //屏蔽鼠标右键
    function window.onhelp(){ return false }
    //屏蔽F1帮助
    function document.onkeydown(){
        if ((window.event.altKey) && ((window.event.keyCode == 37) ||
            //屏蔽Alt+方向键←
            (window.event.keyCode == 39))) {
            //屏蔽Alt+方向键→
            alert("不准你使用ALT+方向键前进或后退网页！"); event.returnValue = false;
        } if ((event.keyCode == 8) ||
            //屏蔽退格删除键
            (event.keyCode == 116) ||
            //屏蔽F5刷新键
            (event.ctrlKey && event.keyCode == 82)) {
            //Ctrl+R
            event.keyCode = 0; event.returnValue = false;
        } if (event.keyCode == 122) { event.keyCode = 0; event.returnValue = false; }
        //屏蔽F11
        if (event.ctrlKey && event.keyCode == 78) event.returnValue = false;
        //屏蔽Ctrl+n
        if (event.shiftKey && event.keyCode == 121) event.returnValue = false;
        //屏蔽shift+F10
        if (window.event.srcElement.tagName == "A" && window.event.shiftKey) window.event.returnValue = false;
        //屏蔽shift加鼠标左键新开一网页
        if ((window.event.altKey) && (window.event.keyCode == 115))}
    //屏蔽Alt+F4
    window.showModelessDialog("about:blank", "", "dialogWidth:1px;dialogheight:1px"); return false; }}
</script>