<script type="text/javascript">
???????//处理键盘事件 禁止后退键（Backspace）密码或单行、多行文本框除外
???????function forbidBackSpace(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;
???????}
???????//禁止后退键 作用于Firefox、Opera
???????document.onkeypress = forbidBackSpace;
???????//禁止后退键 ?作用于IE、Chrome
???????document.onkeydown = forbidBackSpace;
</script>
JS如何禁用浏览器的退格键
原文地址：https://www.cnblogs.com/xieyongbin/p/9685964.html