title: What is the time complexity of HTML DOM lookups
body: <p>Assuming there are no crazy optimizations (I'm looking at you Chrome).</p>
  
  <p>I'm talking about raw, nasty, ain't-broke-don't-fix-it, ie v6 javascript, cost. </p>
  
  <p><strong>The lower limit being:</strong></p>
  
  <pre><code>document.getElementById() 
  </code></pre>
  
  <p><strong>Versus:</strong></p>
  
  <pre><code>document.getElementsByTagName('div') lookup.
  </code></pre>