jsp禁止页面的的text框点backspace页面跳转

//方法一
 var key = new Ext.KeyMap(document,{
  key: 8,
  fn: function(obj,e){
   var type = e.target.type;
   var readonly = e.target.readOnly;
   if(type != 'text' && type != 'textarea' && type != 'password'){
    //e.preventDefault();
    e.stopEvent();
   }
   else if(readonly){
    //e.preventDefault();
    e.stopEvent();
   }
  },
  scope: this
 });
//方法二



Ext.getDoc().on('keydown',function(e){  
    if(e.getKey() == 8 && e.getTarget().type =='text' && !e.getTarget().readOnly){  
          
    }else if(e.getKey() == 8 && e.getTarget().type =='textarea' && !e.getTarget().readOnly){   
      
    }else if(e.getKey() == 8){  
        e.preventDefault();  
    }  
});