复制代码 代码如下:
function banbackspace(e) { 
                var ev = e || window.event;//获取event对象 
                var obj = ev.target || ev.srcelement;//获取事件源 
                var t = obj.type || obj.getattribute('type');//获取事件源类型 
                //获取作为判断条件的事件类型 
                var vreadonly = obj.readonly; 
                var vdisabled = obj.disabled; 
                //处理undefined值情况 
                vreadonly = (vreadonly == undefined) ? false : vreadonly; 
                vdisabled = (vdisabled == undefined) ? true : vdisabled; 
                //当敲backspace键时，事件源类型为密码或单行、多行文本的， 
                //并且readonly属性为true或disabled属性为true的，则退格键失效 
                var flag1 = ev.keycode == 8 && (t == password || t == text || t == textarea) && (vreadonly == true || vdisabled == true); 
                //当敲backspace键时，事件源类型非密码或单行、多行文本的，则退格键失效 
                var flag2 = ev.keycode == 8 && t != password && t != text && t != textarea; 
                //判断 
                if (flag2 || flag1) return false
} 
            //禁止退格键 作用于firefox、opera 
            document.onkeypress = banbackspace; 
            //禁止退格键 作用于ie、chrome 
            document.onkeydown = banbackspace;