Incremental array list with min & max numbers
<p>I'm trying to work through this problem from Codewars and for the life of me cannot figure out what's wrong.  </p>

<p><strong><em>Given the a list of numbers, return the list so that the values increment by 1 for each index up to the maximum value.</em></strong></p>

<p>This is the solution that I've come up with, but it doesn't work for these data sets:  [6, 9] and [-1, 4].  Here's a link to the problem if you'd like to try it yourself:  <a href="http://www.codewars.com/kata/56b29582461215098d00000f/train/javascript" rel="nofollow">codewars - lario &amp; muigi</a></p>

<pre><code>function pipeFix(numbers) {
  var firstNum = numbers[0];
  var lastNum = numbers[numbers.length - 1];
  var iterations = (lastNum - firstNum) + 1;
  var arr = [];
  for (var i = firstNum; i &lt;= iterations; i++) {
    arr.push(i);
  }
  return arr;
}
</code></pre>

<p>If you can point me in the right direction I'd be much obliged.</p>