屏蔽F12 审查元素

/** *   屏蔽F12 审查元素 */    document.onkeydown = function () {        if (window.event && window.event.keyCode == 123) {            alert("F12被禁用");            event.keyCode = 0;            event.returnValue = false;        }        if (window.event && window.event.keyCode == 13) {            window.event.keyCode = 505;        }        if (window.event && window.event.keyCode == 8) {            alert(str + "\n请使用Del键进行字符的删除操作！");            window.event.returnValue = false;        }    }