title: Javascript Not Implemented error
body: <p>I am getting a Not Implemented error when trying to screen the screen-width into a hidden field on page load. Looking at other similar issues, they've all suggested putting everything in variables and making sure I wasn't using reserved words. I have and I am not (that I know of). </p>
  
  <pre><code>function GetScreenWidth() {
      var sWidth = screen.width;
      var hfSw = document.getElementById("&lt;% =hfScreenWidth.ClientID %&gt;");
      hfSw.value = sWidth;
  }
  window.onload = GetScreenWidth();
  </code></pre>
  
  <p>Originally, I was using</p>
  
  <pre><code>function GetScreenWidth() {
      document.getElementById("&lt;% =hfScreenWidth.ClientID %&gt;").value = screen.width;
  }
  </code></pre>
  
  <p>Ultimately, I'm trying to get the screen-width back into the code-behind. If there are better ways to do that, I'd love to hear them.</p>
  
  <p><strong>EDIT:</strong>  the hidden field <strong>is</strong> defined above the  tag.</p>