title: Simple PIN validation
body: <p>Task:
  ATM machines allow 4 or 6 digit PIN codes and PIN codes cannot contain anything but exactly 4 digits or exactly 6 digits.
  If the function is passed a valid PIN string, return true, else return false.</p>
  
  <p>My solution:</p>
  
  <pre><code>function validatePIN (pin) {
    //return true or false
    if (!isNaN(pin) &amp;&amp; Number.isInteger(pin) &amp;&amp; pin.toString().length == 4 || pin.toString().length == 6) { 
      return true 
    } else { 
      return false 
    }
  }
  </code></pre>
  
  <p>The only bug I get is when I pass 4 digits as a string (<code>"1234"</code>) - it equals <code>false</code>.</p>