title: Can setTimeout ever return 0 as the id?
body: <p>I am writing a check to see if a timeout is active. I was thinking of doing this:</p>
  
  <pre><code>var a = setTimeout(fn, 10);
  // ... Other code ... where clearTimeout(a) can be called and set to null
  if (a != null)
  {
     // do soemthing
  }
  </code></pre>
  
  <p>I was wondering if it would ever be possible that a will be 0. In that case I would use <code>a !== null</code></p>