Javascript - How to make auto select another drop down

问题

Here have two list field menu. First brand second item
I want if we select brand IBM that item will select IBM too
In other hand, if we select brand HP that item will select HP too

How to do that in javascript.

<select name="brand">
  <option>Please Select</option>
  <option>IBM</option>
  <option>HP</option>
</select>

<select name="item">
  <option>Please Select</option>
  <option>IBM</option>
  <option>HP</option>  
</select>

回答1:

 <select name="brand" id="brand" onchange="document.getElementById('item').value = document.getElementById('brand').value">
   <option>Please Select</option>
   <option>IBM</option>
   <option>HP</option>
 </select>

 <select name="item" id="item">
   <option>Please Select</option>
   <option>IBM</option>
   <option>HP</option>  
 </select>

回答2:

I noticed your options line up with one another, so you could simply reflect the selectedIndex in in the second from the first:

document.getElementById("brand").onchange = function(){
  document.getElementById("item").selectedIndex = this.selectedIndex;
}

回答3:

You can add an onchange attribute to your brand select element. When a brand is selected, then the selectItem function will be called, which in turn can select the item that matches the value in the item select element. Also, I recommend that you give IDs to your select elements so that you can use document.getElementById("brand").

<select id="brand" name="brand" onchange="selectItem(this.selectedIndex);">
  <option>Please Select</option>
  <option>IBM</option>
  <option>HP</option>
</select>

Here is the DOM reference for the select element: http://www.w3schools.com/jsref/dom_obj_select.asp

来源：https://stackoverflow.com/questions/1974798/javascript-how-to-make-auto-select-another-drop-down

标签

javascript

drop-down-menu

listfield