Sorting Question

// Implement the following functions. Write at least 2
// assertions for each one (the assertions are how you
// will test your code)
//*********************************************************

function lastLetterSort(stringArray) {
  function byLastLetter(a, b) {
    //TODO: implement me. sort the strings in alphabetical
    // order using their last letter
  }
  stringArray.sort(byLastLetter);
}

function sumArray(numberArray) {
  var sum = 0;
  // TODO: implement me using forEach
  return sum;
}

function sumSort(arrayOfArrays) {
  arrayOfArrays.sort(function(item) {
    // TODO: implement me using sumArray
    //  order the arrays based on the sum of the numbers
    //  inside each array
  });
}

if(a < b) {
            return -1;
        } else if(a > b) {
            return 1;
        }

        return 0;

        /* Advanced Solution, inline if */
        // return a < b ? -1 : (a > b ? 1 : 0);
    }
    stringArray.sort(byLastLetter);
}

function sumArray(numberArray) {
    var sum = 0;

    numberArray.forEach(function(number) {
        sum += number;
    });

    return sum;
}

function sumSort(arrayOfArrays) {
    arrayOfArrays.sort(function(a, b) {
        var sumA = sumArray(a),
            sumB = sumArray(b);

        /* Same here like in lastLetterSort */
        /* Basic Solution */
        if(a < b) {
            return -1;
        } else if(a > b) {
            return 1;
        }

        return 0;

        /* Advanced Solution, inline if */
        // return a < b ? -1 : (a > b ? 1 : 0);
    });
}