mergeSort.js

let sorting = (myArray, cb) => {
 let result = mergeSort(myArray);
 return cb(null, result);
};

let mergeSort= (myArray) => {
 if (myArray.length < 2) return myArray;
 let middleIndex = Math.floor(myArray.length/2);

 let firstHalf = myArray.slice(0, middleIndex);
 let secondHalf = myArray.slice(middleIndex, myArray.length);

 return merge(mergeSort(firstHalf), mergeSort(secondHalf));
};

let merge = (myArray1, myArray2) => {
 let result = [];

 while (myArray1.length && myArray2.length) {
 let minimumElement;
 if (myArray1[0] < myArray2[0]) {
 minimumElement = myArray1.shift();
 } else {
 minimumElement = myArray2.shift();
 }
 result.push(minimumElement);
 }

 if (myArray1.length) {
 result = result.concat(myArray1);
 } else {
 result = result.concat(myArray2);
 }

 return result;
};

sorting([6000, 34, 203, 3, 746, 200, 984, 198, 764, 1, 9, 1], (err, sortedArray) => {
 if (err) {

 } else {
 console.log(sortedArray);
 }
});