title: How to add alpha filter to any HTML element and keep the other filters in IE?
body: <p>If I have this HTML</p>
  
  <pre><code>&lt;img src="aaa.png" id="a" style="filter: alpha(opacity=100)"/&gt;
  </code></pre>
  
  <p>Then this javascript works in IE6</p>
  
  <pre><code>document.getElementById("a").filters.alpha.opacity = 60;
  </code></pre>
  
  <p>But if no style is set</p>
  
  <pre><code>&lt;img src="aaa.png" id="a" style=""/&gt;
  </code></pre>
  
  <p>The javascript throws an error <em>'filters.alpha' is null or not an object</em></p>
  
  <p>This code works</p>
  
  <pre><code>document.getElementById("a").style.filter = "alpha(opacity=60)";
  </code></pre>
  
  <p>But then the other filters applied to the image are overwritten. So the question is: <em>How to add alpha filter to any HTML element and keep the other filters in IE?</em></p>
  
  <p><strong>edit</strong> I would like pure javascript (not jQuery) solution</p>