Merge Sort

let mergeSort = function(numbers) {

    function mergeSort(arr) {
        if (arr.length === 1) return arr;
        let center = Math.floor(arr.length / 2);
        let left = arr.slice(0, center);
        let right = arr.slice(center);
        return merge(mergeSort(left), mergeSort(right));
    }
    
    function merge(left, right) {
        let results = [];
        while (left.length && right.length) {
            if (left[0] < right[0]) {
                results.push(left.shift());
            }
            else {
                results.push(right.shift());
            }
        }

        return [...results, ...left, ...right];
    }

    return mergeSort(numbers);
}