How does the first check even pass?... you are accessing ints[-1]... apparently JavaScript does not have a problem with that :)

@AlejandorLazaro if you imply using a hash that's not O(n) algorithm; it's O(n.log(n))

what language?

Does this have a JavaScript solution which takes less than 6 seconds?

Is this more clear?

function largestPairSum(numbers) {
  if (numbers == null || numbers.length < 2) {
    return null; 
  }
  var highest = Number.NEGATIVE_INFINITY;
  var second_highest = Number.NEGATIVE_INFINITY;
  for (var i = 0; i < numbers.length; ++i) {
    if (numbers[i] > highest) { 
      second_highest = highest;
      highest = numbers[i]; 
    }
    else if (numbers[i] > second_highest) { 
      second_highest = numbers[i]; 
    }
  }
  return highest + second_highest;
}