title: js Symbol() usage
body: <p>looking through a polyfill I found Symbols type used like this :</p>
  
  <pre><code>if (window.Symbol) {
    obj = {cached: Symbol(),    /****/ };
  }
  
  /* and is used */
   obj.cached = [] // which overrides Symbol(), 
  </code></pre>
  
  <p>I'm new to <code>Symbol()</code> in JS, but from what I know it should be used for making unique object keys that avoid collision, an so should be used more or less like:</p>
  
  <pre><code>var obj = {}, cached;
  
  if (window.Symbol) {
      cached = Symbol();
      obj[cached] = null;
  }
  /* an then used */
   obj[cached] = [ /*****/ ];
  </code></pre>
  
  <p>Am I missing something?</p>