Merge Sort in Javascript

merge-sort.js

function mergeSort(arr) {
	//base case 
	if (arr.length < 2) return arr;
	var halfLength = Math.ceil(arr.length / 2);
	var leftSide = arr.splice(0, halfLength);
	var rightSide = arr; // just to keep mental model simple
	
	return _stitch(mergeSort(leftSide), mergeSort(rightSide));
}

function _stitch(left, right) {
	var results = [];
	console.log('left is: ', left);
	console.log('right is: ', right);
	while (left.length && right.length) {
		if (left[0] <= right[0]) {
			results.push(left.shift());
		}
		else {
			results.push(right.shift());
		}
	}
	
	while(left.length) {
		results.push(left.shift());
	}
	while(right.length) {
		results.push(right.shift());
	}
	
	return results;
}