JS Merge Sort that sorts by a Object value of choice

Question

Lets get right to it, this is my Code:

function mergeSort(unsortedArray, sortingParameter) {
  if (unsortedArray.length <= 1) {
    return unsortedArray;
  }

  const middle = Math.floor(unsortedArray.length / 2);

  const left = unsortedArray.slice(0, middle);
  const right = unsortedArray.slice(middle);

  // Using recursion to combine the left and right

  return merge(mergeSort(left), mergeSort(right), sortingParameter);
}

function merge(left, right, sortingParameter) {
  let resultArray = [],
    leftIndex = 0,
    rightIndex = 0;

  if (sortingParameter) {
    console.log(left[2][sortingParameter], "parameterCheck");
    while (leftIndex < left.length && rightIndex < right.length) {
      console.log("while");
      if (
        left[leftIndex][sortingParameter] < right[rightIndex][sortingParameter]
      ) {
        resultArray.push(left[leftIndex]);
        leftIndex++;
      } else {
        resultArray.push(right[rightIndex]);
        rightIndex++;
      }
    }
  } else {
    while (leftIndex < left.length && rightIndex < right.length) {
      if (left[leftIndex] < right[rightIndex]) {
        resultArray.push(left[leftIndex]);
        leftIndex++;
      } else {
        resultArray.push(right[rightIndex]);
        rightIndex++;
      }
    }
  }

  return resultArray
    .concat(left.slice(leftIndex))
    .concat(right.slice(rightIndex));
}

export { mergeSort };

I am new to algorithms so I am not sure it's not an obvious error, but I am trying to sort a comments Object structured like this

{
likeCount: integer,
prop: "moreStuff"
}

By the integer value stored at the likeCount key... when I put in an Array of Integers without a sorting parameter this function works just fine for example

[9,5,7,3,1] => [1,3,5,7,9]

This is a big headache for me thank you for the help in advance!!!

Answer 1

You forgot to pass the sortingParameter in recursive call of mergeSort, see snippet

function mergeSort(unsortedArray, sortingParameter) {
  if (unsortedArray.length <= 1) {
    return unsortedArray;
  }

  const middle = Math.floor(unsortedArray.length / 2);

  const left = unsortedArray.slice(0, middle);
  const right = unsortedArray.slice(middle);

  // Using recursion to combine the left and right

  return merge(mergeSort(left, sortingParameter), mergeSort(right, sortingParameter), sortingParameter);
}

function merge(left, right, sortingParameter) {
  let resultArray = [],
    leftIndex = 0,
    rightIndex = 0;

  if (sortingParameter) {
    while (leftIndex < left.length && rightIndex < right.length) {
      if (left[leftIndex][sortingParameter] < right[rightIndex][sortingParameter]) {
        resultArray.push(left[leftIndex]);
        leftIndex++;
      } else {
        resultArray.push(right[rightIndex]);
        rightIndex++;
      }
    }
  } else {
    while (leftIndex < left.length && rightIndex < right.length) {
      if (left[leftIndex] < right[rightIndex]) {
        resultArray.push(left[leftIndex]);
        leftIndex++;
      } else {
        resultArray.push(right[rightIndex]);
        rightIndex++;
      }
    }
  }

  return resultArray
    .concat(left.slice(leftIndex))
    .concat(right.slice(rightIndex));
}


console.log(mergeSort([{
  count: 4,
  val: "A"
}, {
  count: 7,
  val: "B"
}, {
  count: 9,
  val: "C"
}, {
  count: 12,
  val: "D"
}, {
  count: 3,
  val: "E"
}, {
  count: 6,
  val: "F"
}, {
  count: 7,
  val: "G"
}, {
  count: 5,
  val: "H"
}], "count"));