직접 실행해봤는데 약간 느린 경향은 있는데 2배 까진 아닌 것 같아요.

function quickSortInPlace(arr, left = 0, right = arr.length - 1) {  
    if (left >= right) return;  
  
    const pivotIndex = partition(arr, left, right);  
    quickSortInPlace(arr, left, pivotIndex - 1);  
    quickSortInPlace(arr, pivotIndex + 1, right);  
}  
  
function partition(arr, left, right) {  
    const pivot = arr[right];  
    let i = left;  
  
    for (let j = left; j < right; j++) {  
        if (arr[j] < pivot) {  
            [arr[i], arr[j]] = [arr[j], arr[i]];  
            i++;  
        }  
    }  
  
    [arr[i], arr[right]] = [arr[right], arr[i]];  
    return i;  
}  
  
function quickSort(arr) {  
    if (arr.length <= 1) return arr;  
  
    const pivot = arr[arr.length - 1];  
    const left = [];  
    const right = [];  
  
    for (let i = 0; i < arr.length - 1; i++) {  
        if (arr[i] < pivot) {  
            left.push(arr[i]);  
        } else {  
            right.push(arr[i]);  
        }  
    }  
  
    return [...quickSort(left), pivot, ...quickSort(right)];  
}  
  
// =============  
  
function quickSortGPT(arr) {  
    if (!Array.isArray(arr)) {  
        throw new TypeError('quickSort expects an array');  
    }  
    if (arr.length <= 1) return [...arr];  
  
    const pivot = arr[Math.floor(arr.length / 2)];  
    const left = [];  
    const equal = [];  
    const right = [];  
  
    for (const el of arr) {  
        if (el < pivot) left.push(el);  
        else if (el > pivot) right.push(el);  
        else equal.push(el);  
    }  
  
    return [...quickSortGPT(left), ...equal, ...quickSortGPT(right)];  
}  
  
function quickSortInPlaceGPT(arr) {  
    if (!Array.isArray(arr)) {  
        throw new TypeError('quickSortInPlace expects an array');  
    }  
  
    const stack = [[0, arr.length - 1]];  
  
    while (stack.length) {  
        const [lo, hi] = stack.pop();  
        if (lo >= hi) continue;  
  
        const pivotIndex = partitionGPT(arr, lo, hi);  
  
        // Tail‑recursion elimination: push larger partition first  
        if (pivotIndex - 1 - lo > hi - (pivotIndex + 1)) {  
            stack.push([lo, pivotIndex - 1]);  
            stack.push([pivotIndex + 1, hi]);  
        } else {  
            stack.push([pivotIndex + 1, hi]);  
            stack.push([lo, pivotIndex - 1]);  
        }  
    }  
    return arr;  
}  
  
function medianOfThreeGPT(a, b, c) {  
    return (a - b) * (c - a) >= 0 ? a  
        : (b - a) * (c - b) >= 0 ? b  
            : c;  
}  
  
function partitionGPT(arr, lo, hi) {  
    const mid = lo + ((hi - lo) >> 1);  
    const pivotValue = medianOfThreeGPT(arr[lo], arr[mid], arr[hi]);  
  
    while (true) {  
        while (arr[lo] < pivotValue) lo++;  
        while (arr[hi] > pivotValue) hi--;  
  
        if (lo >= hi) return hi;  
  
        [arr[lo], arr[hi]] = [arr[hi], arr[lo]];  
        lo++;  
        hi--;  
    }  
}  
  
function testQuicksort(qs, qsp) {  
    const repeat = 100;  
    const arrLength = 100000;  
    const unsortedArray = new Array();  
    for (let i = 0; i < arrLength; i++)  
        unsortedArray.push(Math.round(Math.random() * arrLength));  
  
    let sorted = [];  
  
    const qb = performance.now();  
    for (let i = 0; i < repeat; i++)  
        sorted = qs(unsortedArray);  
    const qe = performance.now();  
  
    const rqb = performance.now();  
    for (let i = 0; i < repeat; i++) {  
        let copied = [...unsortedArray];  
        qsp(copied);  
    }  
    const rqe = performance.now();  
  
    // 소수점 2자리 까지  
    const p1 = ((qe - qb) / repeat).toFixed(2);  
    const p2 = ((rqe - rqb) / repeat).toFixed(2);  
    
    console.log(`Quicksort: ${p1} ms, In-place: ${p2} ms`);  
}  
  
function main() {  
    const useGPT = process.argv.includes('--gpt');  
    console.log(`Using ${useGPT ? 'GPT' : 'geekNews'} quicksort implementation.`);  
    if (useGPT) {  
        testQuicksort(quickSortGPT, quickSortInPlaceGPT);  
    } else {  
        testQuicksort(quickSort, quickSortInPlace);  
    }  
}  
  
main();  

===
node q.js
Using geekNews quicksort implementation.
Quicksort: 29.55 ms, In-place: 9.94 ms
node q.js
Using geekNews quicksort implementation.
Quicksort: 28.42 ms, In-place: 9.07 ms
node q.js
Using geekNews quicksort implementation.
Quicksort: 26.91 ms, In-place: 9.15 ms
node q.js --gpt
Using GPT quicksort implementation.
Quicksort: 28.73 ms, In-place: 9.22 ms
node q.js --gpt
Using GPT quicksort implementation.
Quicksort: 26.87 ms, In-place: 9.22 ms
node q.js --gpt
Using GPT quicksort implementation.
Quicksort: 27.97 ms, In-place: 9.30 ms
node --version
v22.14.0

bun q.js
Using geekNews quicksort implementation.
Quicksort: 32.05 ms, In-place: 17.39 ms
bun q.js
Using geekNews quicksort implementation.
Quicksort: 30.97 ms, In-place: 17.82 ms
bun q.js
Using geekNews quicksort implementation.
Quicksort: 29.73 ms, In-place: 16.14 ms
bun q.js --gpt
Using GPT quicksort implementation.
Quicksort: 30.61 ms, In-place: 12.63 ms
bun q.js --gpt
Using GPT quicksort implementation.
Quicksort: 31.09 ms, In-place: 12.76 ms
bun q.js --gpt
Using GPT quicksort implementation.
Quicksort: 33.24 ms, In-place: 12.75 ms
bun --version
1.2.14

deno q.js
Using geekNews quicksort implementation.
Quicksort: 32.30 ms, In-place: 6.79 ms
deno q.js
Using geekNews quicksort implementation.
Quicksort: 26.79 ms, In-place: 6.86 ms
deno q.js
Using geekNews quicksort implementation.
Quicksort: 26.09 ms, In-place: 6.85 ms
deno q.js --gpt
Using GPT quicksort implementation.
Quicksort: 27.18 ms, In-place: 7.92 ms
deno q.js --gpt
Using GPT quicksort implementation.
Quicksort: 25.34 ms, In-place: 8.12 ms
deno q.js --gpt
Using GPT quicksort implementation.
Quicksort: 25.39 ms, In-place: 8.09 ms
deno --version
deno 2.3.3 (stable, release, x86_64-pc-windows-msvc)
v8 13.7.152.6-rusty
typescript 5.8.3