function banBackSpace(e) {
var ev = e || window.event;//Gets the event object & cake;
var obj = ev.target || ev.srcElement;//Getting the source of the event & NBSP;
var t = obj.type || obj.getAttribute('type');//Gets the event source type & NBSP;
//Gets the type of event & NBSP; that is a judgment condition;
var vReadOnly = obj.readOnly;
var vDisabled = obj.disabled;
//Dealing with the undefined situation & sponge;
vReadOnly = (vReadOnly == undefined) ? false : vReadOnly;
vDisabled = (vDisabled == undefined) ? true : vDisabled;
//When the Backspace key is struck, the event source type is password or single-line, multi-line text, & NBSP;
//If the readOnly property is true or the disabled property is true, the backspace key is invalid & PI.
var flag1 = ev.keyCode == 8 && (t == "password" || t == "text" || t == "textarea") && (vReadOnly == true || vDisabled == true);
//When the Backspace key is struck, the Backspace key is invalidate if the event source type is not password or if it is a single line, multi-line text.
var flag2 = ev.keyCode == 8 && t != "password" && t != "text" && t != "textarea";
//Judge
if (flag2 || flag1) return false
}
//Disable the backspace key for Firefox, Opera
document.onkeypress = banBackSpace;
//Disable backspace key on IE, chrome & cake;
document.onkeydown = banBackSpace;