javascript禁制后退键(Backspace)实例代码_javascript技巧

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;