title: update Html.TextBoxFor "readonly" attribute on and off
body: <p>I'm srugelling with this,
  Working on MVC, upon change on Html.TextBoxFor value I want to change a readonly attribute of another Html.TextBoxFor.
  I tried several ways-using IE it does not work.
  here some code:</p>
  
  <pre><code>@Html.TextBoxFor(x =&gt; x.NumberOfQuestion, new { id = "ExamOptions", onchange = "javascript:ReadOnlyHandle();" })
  
  &lt;script&gt;
      function ReadOnlyHandle() {
          //document.getElementById("NoDiffNum").readOnly = true;
          var startHSelect = document.getElementById("NoDiffNum");
          debugger;
          startHSelect.setAttribute("readonly", "true");
      }
      debugger;
  &lt;/script&gt;
  </code></pre>
  
  <p>and the row in a table I would like to change:</p>
  
  <pre><code>&lt;td id="NoDiffNum"&gt;@Html.TextBoxFor(model =&gt; model.Topics[i].NumberOfNoDifficulltySet)&lt;/td&gt;
  </code></pre>
  
  <p>the readonly attribute did not changed - 
  any help is most welcome!</p>