title: CoffeeScript Undefined
body: <p>In javascript to check if a variable was never created, we just do  </p>
  
  <pre><code>if (typeof MyVariable !== "undefined"){ ... }
  </code></pre>
  
  <p>I was wonder how I do that in coffeescript?... I try something like</p>
  
  <pre><code>if (MyVariable?false){ ... }
  </code></pre>
  
  <p>but this check if <code>MyVariable</code> is a function if so that will call MyVariable(false) if not that will call void(0) or something like that.</p>