Question

In the following HTML code I would like to realize the following with JavaScript. When the user selects Audi, he has only the option to select application 2 (application 1 has to disappear in this case).

<select>
    <option value="volvo">Volvo</option>
    <option value="audi">Audi</option>
</select>
<select>
    <option value="app1">application 1</option>
    <option value="app2">application 2</option>
</select>

I wrote the code here.

Answer 1

html:

 <select>
  <option id="app1" value="volvo">Volvo</option>
  <option id="app2" value="audi">Audi</option>
  </select>
 <select>
  <option value="app1">application 1</option>
  <option value="app2">application 2</option>
</select>

js:

var selections = document.getElementsByTagName('select');
selections[0].onchange = carSelection;

function carSelection(e) {
    var first = selections[0];
    var id = first.options[first.selectedIndex].id;

    var second = selections[1];
    var  j = 0;
    while (second.options[j])  {
        second.options[j].disabled = (second.options[j].value != id );
        if (second.options[j].value == id)
            second.selectedIndex = j;
        j++;
    }    
}

http://jsfiddle.net/U4y2J/3/