Find missing numbers in an array of numbers

findMissingNums.js

// Solution:    sort numbers first, then test the offset(s)
// Disclosure:  this is not a great idea for 4 billion numbers 
//              and is completely inefficient
var numArray = [ 2, 3, 1, 5, 7, 10 ];

var findMissingNumbers = function (numArray)
{
  var missing = [];

  numArray.sort(
    function (a, b)
    {
      return (a - b);
    }
  );

  for (var i = 0 ; i < numArray.length ; i++)
  {
    if (numArray[i + 1] - numArray[i] > 1)
    {
      missing.push (numArray[i + 1] - numArray[i]);
    }
  }

  return missing;
};