title: How to idiomatically initialize to zero or increment a property?
body: <p>I love those short js oneliners. I'd like to know if there's something logical and elegant for: </p>
  
  <ul>
  <li>intializing a variable to zero if undefined</li>
  <li>increment by one otherwise.</li>
  </ul>
  
  <p>Shorter than this preferrably ;)</p>
  
  <pre><code>var obj = {} ; 
  
  //some iterative called function
  obj.prop = obj.prop===undefined?0:obj.prop++;
  </code></pre>