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;
        }
    }