title: Change the query string of an iframe src when select options are clicked
body: <p>I have several dropdown boxes on a site and I need to append/add/remove query string depending on what the user has chosen.  How can I accomplish it?  Here is some generic code for demo purposes:</p>
  
  <pre><code>&lt;select name="status" onchange="document.getElementById('Iframe2').src = document.getElementById('Iframe2').src + this.options[this.selectedIndex].value"&gt;
  &lt;option&gt;&lt;/option&gt;
  &lt;option value="&amp;A=1"&gt;1&lt;/option&gt;
  &lt;option value="&amp;A=2"&gt;2&lt;/option&gt;
  &lt;/select&gt;
  
  
  &lt;select name="plan" onchange="document.getElementById('Iframe2').src = document.getElementById('Iframe2').src + this.options[this.selectedIndex].value"&gt;
  &lt;option&gt;&lt;/option&gt;
  &lt;option value="&amp;FilterGarage=Right"&gt;Right&lt;/option&gt;
  &lt;option value="&amp;FilterGarage=Left"&gt;Left&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>So what I would like to happen is let's say the user selects the "1" option and then the "Right" option.  The way I have it now, it works fine.  The problem happens when the user then goes back and changes the "Right" option to "Left".  At that point what's happening is it's just adding another &amp;FilterGarage parameter and ends up not showing anything.</p>
  
  <p>I guess what I need to know is how to remove the option value and regenerate it depending on what the user picks each time.</p>