merge sort not working – Javascript code : not able to find error even after debugging

I am trying to understand all sorting algos and this is the code I have written for merge sort, but its not working, can you please point out the error in it :

solve: function (A) {
    let count = this.mergeSort(A);
    return count;
},
mergeTwoSortedArrays: function (A, B) {
    let i = 0;
    let j = 0;
    let k = 0;
    let C = [];
    while (i < A.length && j < B.length && A[i] || B[j]) {
        if (A[i] < B[j]) {
            C[k] = A[i];
            i++;
            k++;
        }
        else {
            C[k] = B[j];
            j++;
            k++;
        }

    }
    while (j < B.length) {
        C[k] = B[j];
        k++;
        j++;
    }
    while (i < A.length) {
        C[k] = A[i];
        k++;
        i++;
    }
    return C;
},
mergeSort: function (a) {
    let n = a.length;
    if (n <= 1) return a;
    let c = Array.from({ length: Math.floor(n / 2) }, (_, i) => a[i]);
    let d = Array.from({ length: n - c.length }, (_, i) => a[c.length + i]);
    return this.mergeTwoSortedArrays(c, d);
}

Well the question is asking me to add more details for my post to be approved.
So my approach here is : divide the array into two equal parts until they become array of 1 element and then use merge technique to merge two sorted arrays.

>Solution :

You should simply check i < A.length && j < B.length as the loop condition.

Here is your updated code:

const mergeSort = {
  solve: function (A) {
    return this.mergeSortFunction(A);
  },
  mergeTwoSortedArrays: function (A, B) {
    let i = 0;
    let j = 0;
    let k = 0;
    let C = [];
    while (i < A.length && j < B.length) {
      if (A[i] < B[j]) {
        C[k] = A[i];
        i++;
        k++;
      } else {
        C[k] = B[j];
        j++;
        k++;
      }
    }
    while (j < B.length) {
      C[k] = B[j];
      k++;
      j++;
    }
    while (i < A.length) {
      C[k] = A[i];
      k++;
      i++;
    }
    return C;
  },
  mergeSortFunction: function (a) {
    let n = a.length;
    if (n <= 1) return a;
    let c = Array.from({ length: Math.floor(n / 2) }, (_, i) => a[i]);
    let d = Array.from({ length: n - c.length }, (_, i) => a[c.length + i]);
    return this.mergeTwoSortedArrays(this.mergeSortFunction(c), this.mergeSortFunction(d));
  }
};

// Example
const inputArray = [38, 27, 43, 3, 9, 82, 10];
const sortedArray = mergeSort.solve(inputArray);
console.log(sortedArray); 
// Output: [3, 9, 10, 27, 38, 43, 82]