MergeSort.js

/*
	Merge Sort in JavaScript.
*/
function merge(arr) {
	if (arr.length <= 1) {
		return arr;
	}
	const left = merge(arr.slice(0, arr.length / 2));
	const right = merge(arr.slice((arr.length / 2), arr.length));
	const leftIterator = mergeHelper(left)
	const rightIterator = mergeHelper(right)
	return mergeSort(leftIterator,rightIterator);
}

function mergeSort(leftIterator, rightIterator) {
	const newLst = [];
	let leftItem = leftIterator.next()
	let rightItem = rightIterator.next()
	while (!leftItem.done && !rightItem.done) {
		if (leftItem.value < rightItem.value) {
			newLst.push(leftItem.value);
			leftItem = leftIterator.next();
			continue;
		}
		newLst.push(rightItem.value);
		rightItem = rightIterator.next();
	}

	const leftItems = !leftItem.done ? [leftItem.value, ...leftIterator] : []
	const rightItems = !rightItem.done ? [rightItem.value, ...rightIterator] : []

	return [...newLst, ...leftItems, ...rightItems];
}

function* mergeHelper(items) {
	yield* items;
}

const merger = (arr) => merge(arr);
module.exports = merger;