二路归并排序

        var arr = [49, 38, 65, 97, 76, 13, 27, 48, 55, 4];

        function MergeSort(arr) {
            var len = arr.length;
            if(len<=1){ return arr; }
            var middle = Math.floor(len/2);
            var left = arr.slice(0,middle);
            var right = arr.slice(middle)
            return merge(MergeSort(left),MergeSort(right));
        }
        function merge(left,right){
            var result = [];
            while(left.length && right.length){
                if(left[0]<=right[0]){
                    result.push(left.shift())
                }else{
                    result.push(right.shift())
                }
            }
            while(left.length){
                result.push(left.shift())
            }
            while(right.length){
                result.push(right.shift())
            }
            return result;
        }
        console.log(MergeSort(arr)); //4, 13, 27, 38, 48, 49, 55, 65, 76, 97