mergesort.js

/**
 * 
 * @param {unknown[]} arr 
 * @return {unknown[]}
 */
function mergeSort(arr) {
    if (arr.length === 1) {
        return arr;
    }

    const indexMiddle = Math.trunc(arr.length / 2);
    const left = arr.slice(0, indexMiddle);
    const right = arr.slice(indexMiddle);

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

/**
 * 
 * @param {unknown[]} left 
 * @param {unknown[]} right
 */
function merge(left, right) {
    let result = [];
    let indexLeft = 0;
    let indexRight = 0;

    while (indexLeft < left.length && indexRight < right.length) {
        const lefty = left[indexLeft];
        const righty = right[indexRight];

        if (lefty < righty) {
            result.push(lefty);
            indexLeft++;
        } else {
            result.push(righty);
            indexRight++;
        }
    }

    const unpushedLeft = left.slice(indexLeft);
    const unpushedRight = right.slice(indexRight);

    console.debug({ result }, { indexLeft, unpushedLeft }, { indexRight, unpushedRight })

    return [...result, ...unpushedLeft, ...unpushedRight];
}

const list = [2, 5, 1, 3, 7, 2, 3, 8, 6, 3]
console.log(mergeSort(list)) // [ 1, 2, 2, 3, 3, 3, 5, 6, 7, 8 ]

quicksort.js

/**
 * 
 * @param {unknown[]} arr 
 * @return {unknown[]}
 */
function quickSort(arr) {
    if (arr.length < 2) {
        return arr;
    }

    const pivot = arr[0];
    const left = [];
    const right = [];

    const listLength = arr.length;
    for (let i = 1; i < listLength; i++) {
        const value = arr[i];
        if (value < pivot) {
            left.push(value);
        } else {
            right.push(value);
        }
    }
    return [...quickSort(left), pivot, ...quickSort(right)];
};

const list = [2, 5, 1, 3, 7, 2, 3, 8, 6, 3]
console.log(quickSort(list)) // [ 1, 2, 2, 3, 3, 3, 5, 6, 7, 8 ]