javascript 禁止backspace返回上一级
$(document).keydown(function(e){
var target = e.target ;
var tag = e.target.tagName.toUpperCase();
if(e.keyCode == 8){
if((tag == 'INPUT' && !$(target).attr("readonly"))||(tag == 'TEXTAREA' && !$(target).attr("readonly"))){
if((target.type.toUpperCase() == "RADIO") || (target.type.toUpperCase() == "CHECKBOX")){
return false ;
}else{
return true ;
}
}else{
return false ;
}
}
});