title: Codility "PermMissingElem" Solution in Javascript
body: <p>A codility problem asks to find the missing number in zero-indexed array A consisting of N different integers.</p>
  
  <p>E.g.</p>
  
  <pre><code>  Arr[0] = 2
    Arr[1] = 3
    Arr[2] = 1
    Arr[3] = 4
    Arr[4] = 6
  </code></pre>
  
  <p>I previously submitted a solution that first sorts the array and then performs a forEach function returning the value +1 where the array difference between elements is more than 1, however this doesn't get the 100 points.</p>
  
  <p>Is there a way to improve this?</p>