title: Check if variable is false and not either true or undefined
body: <p>What's the best way to check if <code>myvar</code> javascript <code>variable === false</code> or not (it may be undefined as well).</p>
  
  <pre><code>if (myvar === false)
  </code></pre>
  
  <p>would be fine but <code>myvar</code> it could be undefined. Only <code>false</code> value is acceptable, not undefined.</p>
  
  <p>Any shorter than <code>if (typeof myvar !== "undefined" &amp;&amp; myvar === false)</code>?</p>