Dropdown currentIndex onchange

there is a dropdown with 5 options. Currently,option 2 is selected.The user selects option 4 now.The onchange event gets fired which is caught in a JS function listening for onchange on the select.

In the JS function, I can check easily the index of the option selected by the user using the selectedIndex property.However, I want to also know what was the original value that the user changed it from.

Is there a property that persists basically the original value ie option 2 in this case.

---

Just as a concept I put together the following - there may very well be a better way to do this:

var vals = [];

document.getElementById("colors").onchange = function(){
   vals.unshift(this.selectedIndex);
};

function getPrevious(){
  alert(vals[1]); // you'll need more logic here
                  // this is purposefully simplistic
}

--

<select id="colors">
   <option>Red</option>
   <option>Green</option>
   <option>Blue</option>
</select>

Closed-up Example:

I've tried to tie this all into the actual drop-down element itself. In all honesty, this is the first time I've ever add functions to the dropdown itself, so I cannot promise that this won't have consequences:

   var colors = document.getElementById("colors");
       colors.vals = [];
       colors.setPrevious = function() { this.vals.unshift(this.selectedIndex); }
       colors.getPrevious = function() { return this.vals[1]; }
       colors.onchange    = function() { this.setPrevious(); this.getPrevious(); }
       // set initial state
       colors.setPrevious();

---

正如dl所说的那样，您可以使用简单的隐藏变量来保存该值。我们可以将当前值设置为隐藏变量。

<input type = "hidden" id = "previous" name = "previous"></input>

---

不，你需要坚持自己在一个JS变量。

链接地址: http://www.djcxy.com/p/43966.html

上一篇: 像JavaScript中的对象

下一篇: 下拉currentIndex onchange