title: Check for an empty map
body: <p>I'm having an interesting issue that I'm sure is easily explained, but the explanation is eluding me.</p>
  
  <p>An undefined or null object in javascript is equal to false.
  </p>
  
  <pre><code>var x;
  alert(!x); //returns true
  alert(x==true); //returns false
  </code></pre>
  
  <p>What about an empty array object? Is that the equivalent of true or false?</p>
  
  <pre><code>var x = [];
  alert (x==true); //returns false
  alert (!x); //returns false
  </code></pre>
  
  <p>If it is equivalent to true, how do I check if it's non-empty? I was hoping to do</p>
  
  <pre><code>if (!x) {
      //do stuff
  }
  </code></pre>
  
  <p>I tried checking <code>x.length</code>, but I'm using this object as a map:</p>
  
  <pre><code>var x = [];
  alert(x.length); //returns 0
  x.prop = "hello"; 
  alert(x.length); //still returns 0
  </code></pre>
  
  <p>How can I check if my map is empty?</p>