アルゴリズムを統合する

	function merge(left, right){
            var result = [];
            while (left.length > 0 && right.length > 0) {
               if(left[0] < right[0]){
                    result.push(left.shift());
               }else{
                    result.push(right.shift());
               }   
            }
               //console.log(result);
               //[1 2 3]
             return result.concat(left).concat(right);
        } 
        function mergeSort(arr) {
            if(arr.length == 1) { 
                return arr; 
            }
            var mid = Math.floor(arr.length / 2);
            var left_arr = arr.slice(0, mid);
            var right_arr = arr.slice(mid);
            //console.log(right_arr);
            return merge(mergeSort(left_arr), mergeSort(right_arr));
        }
        //merge([2],[1,3])
        var arr = [2, 1, 3];

        console.log(mergeSort(arr));