JavaScript 修改表单样式和readOnly属性

function change() {
       var obj = document.getElementById("condition1");//得到下拉列框对象
          var index = obj.selectedIndex;//得到下拉列表的下标0,1,2,3,
          var val = obj.options[index].value;//得到下拉列表的value
          var text = obj.options[index].text;//得到下拉列表的text
         //alert(obj);
         alert(index);
         //alert(val);
         //alert(text);
          if (val == 0){
              alert("请选择条件！");
          }else {
              if(val == 1) {
                  document.getElementById("condition2").style.backgroundColor = "#c0c0c0";//修改input的背景颜色
                  document.getElementById("condition2").readOnly = true;//修改input的readOnly属性
              }
              else {
                  var obj2 = document.getElementById("condition2");
                  obj2.style.backgroundColor = "#ffffff";
                  document.getElementById("condition2").readOnly = false;
              }
          }
      }