title: disable checkbox when i select
body: <p>i have a problem in html and javascript. i have tried different approach but everything didnt worked. so this is my sample code.</p>
  
  <pre><code>    &lt;select id = "testselect" name = "testselect"&gt;
          &lt;option&gt; &lt;/option&gt;
          &lt;option id = "o1" name = "testselect" value = "1"  onselect='document.getElementById("os1").disabled = true;'&gt; 1 &lt;/option&gt;
          &lt;option id = "o2"  name = "testselect" value = "2" &gt; 2 &lt;/option&gt;
          &lt;option id = "o3" name = "testselect" value = "3"&gt; 3 &lt;/option&gt;
       &lt;/select&gt;
  
  
       &lt;div &gt; 
          &lt;input id = "os1"  type="checkbox" name="othser[]" value="7000" /&gt;cb1&lt;br/&gt;
          &lt;input id = "os2"  type="checkbox" name="othser[]" value="7001"/&gt;cb2&lt;br/&gt;
          &lt;input id = "os3"  type="checkbox" name="othser[]" value="7002"/&gt;cb3&lt;br/&gt;
       &lt;/div&gt;
  </code></pre>
  
  <p>ok, that's the code. what i want to happen is, when i selected o1(option id), os1(checkbox id) must be disabled and when i selected o2(option id), os2(checkbox id) must be disabled, and so on. so can anyone help me? </p>