title: What's the efficiency in Big O notation of the "in" operator or obj.hasOwnProperty(prop)
body: <p>Mozilla's website clearly describes <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/hasOwnProperty" rel="noreferrer"><code>hasOwnProperty()</code></a> and the <a href="https://developer.mozilla.org/en/JavaScript/Reference/Operators/Special/in" rel="noreferrer"><code>in</code></a> operator.</p>
  
  <p>However, it does not give any implementation details in regards to their efficiencies.</p>
  
  <p>I would suspect they'd be <code>O(1)</code> (constant time) but would love to see any references or tests that might exist.</p>