SOURCE

function ArrayList() {
    let array = [5, 4, 3, 2, 1];

    const merge = function (left, right) {
        console.log('merge----', left, right)
        let result = [];
        let il = 0;
        let ir = 0;

        while(il < left.length && ir < right.length) {
            if (left[il] < right[ir]) {
                result.push(left[il++]);
            } else {
                result.push(right[ir++]);
            }
        }

        while(il < left.length) {
            result.push(left[il++]);
        }

        while(ir < right.length) {
            result.push(right[ir++]);
        }
        console.log('merge--', result)
        return result;
    }

    const mergeSortRec = function (array) {
        console.log('---', array)
        const length = array.length;
        if (length === 1) {
            return array;
        }

        const mid = Math.floor(length / 2);
        const left = array.slice(0, mid);
        const right = array.slice(mid, length);

        return merge(mergeSortRec(left), mergeSortRec(right));
    }

    this.mergeSort = function() {
        array = mergeSortRec(array)
        return array
    }
}

const al = new ArrayList()
console.log(al.mergeSort())