Merge Sort

merge-sort.js

function merge(arrA, arrB) {
    let idxA=0, idxB=0, result=[];

    while(idxA < arrA.length || idxB < arrB.length) {

        if(idxB === arrB.length || arrA[idxA] <= arrB[idxB]) {
            result.push(arrA[idxA]);
            idxA++;
        }else if(idxA === arrA.length || arrB[idxB] <= arrA[idxA]) {
            result.push(arrB[idxB]);
            idxB++;
        }
    }

    return result;
}

function mergeSort(array) {
    let len = array.length;

    let middle = parseInt(len / 2);

    let left = array.slice(0, middle);
    let right = array.slice(middle, len);

    left = left.length > 1 ? mergeSort(left) : left;
    right = right.length > 1 ? mergeSort(right) : right;

    return merge(left, right);
}

console.log(mergeSort([9, 6, -7, 4, 9, 4, 6, 9, 7, -7]));