QuickSort implementation in JavaScript

quick-sort.js

function quickSort(arr, start = 0, end = arr.length - 1) {
    if (start < end) {
		const sortedIndex = partition(arr, start, end);

		quickSort(arr, start, sortedIndex-1);
		quickSort(arr, sortedIndex+1, end);
	}
}

function swap(arr, a, b) {
	let temp = arr[a];
	arr[a] = arr[b];
	arr[b] = temp;
}

function partition(arr, start, end) {
	let pivotIndex =  start + Math.ceil((end - start) / 2); // or simply end
	const pivot = arr[pivotIndex];

	let sortedIndex = start - 1;

	for(let j = start; j <= end; j++) {
		const currentValue = arr[j];
		if(currentValue < pivot) {
			sortedIndex++;
			swap(arr, sortedIndex, j);
			if(sortedIndex === pivotIndex) {
				pivotIndex = j;
			} else if(j === pivotIndex) {
				pivotIndex = sortedIndex;
			}
		}
	}
	sortedIndex++;
	swap(arr, sortedIndex, pivotIndex);
	return sortedIndex;
}

/*
const array = [10, 80, 30, 90, 40, 50, 70];
quickSort(array);
console.log(array);
*/