禁用返回键

document.documentElement.onkeydown = function (evt) {


//获取事件对象 
var elem = event.relatedTarget || event.srcElement || event.target || event.currentTarget;

if (event.keyCode == 8) {//判断按键为backSpace键

//获取按键按下时光标做指向的element 
var elem = event.srcElement || event.currentTarget;

//判断是否需要阻止按下键盘的事件默认传递 
var name = elem.nodeName;

if (name != 'INPUT' && name != 'TEXTAREA') {
return _stopIt(event);
}
var type_e = elem.type.toUpperCase();
if (name == 'INPUT' && (type_e != 'TEXT' && type_e != 'TEXTAREA' && type_e != 'PASSWORD' && type_e != 'FILE')) {
return _stopIt(event);
}
if (name == 'INPUT' && (elem.readOnly == true || elem.disabled == true)) {
return _stopIt(event);
}
}

 

}
function _stopIt(e) {
if (e.returnValue) {
e.returnValue = false;
}
if (e.preventDefault) {
e.preventDefault();
}

return false;
}