add merge_sort.js, fix README layout

Author: yennanliu

README.md

@@ -98,13 +98,13 @@
 ||Breadth-first search (BFS)| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/bfs.py), [JS](https://github.com/yennanliu/CS_basics/blob/master/algorithm/js/bfs.js)|`FIND SHORTEST PATH`|| AGAIN***| 
 ||Depth-first search (DFS) |[Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/dfs.py), [JS](https://github.com/yennanliu/CS_basics/blob/master/algorithm/js/dfs.js)| `TO CHECK IF SOMETHING EXIST`| `inorder`, `postorder`, `postorder (can recreate a tree)`| AGAIN***| 
 ||Bubble sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/bubble_sort.py), [JS](https://github.com/yennanliu/CS_basics/blob/master/algorithm/js/bubble_sort.js) , [C](https://github.com/yennanliu/CS_basics/blob/master/algorithm/c/bubble_sort.c)| | | OK* (3)|  
-||Insertion sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/insertion_sort.py), [JS](https://github.com/yennanliu/CS_basics/blob/master/algorithm/js/insertion_sort.js)  | | |AGAIN| 
+||Insertion sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/insertion_sort.py), [JS](https://github.com/yennanliu/CS_basics/blob/master/algorithm/js/insertion_sort.js) || work very fast for `nearly sorted` array|AGAIN| 
 ||Bucket sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/bucket_sort.py)  | | |AGAIN| 
 ||Quick sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/quick_sort.py)| | | AGAIN***| 
 ||Heap sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/heap_sort.py)| | | AGAIN**| 
-||Merge sort|[Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/merge_sort.py)  | | | OK* (2)| 
+||Merge sort|[Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/merge_sort.py), [JS](https://github.com/yennanliu/CS_basics/blob/master/algorithm/js/merge_sort.js)  | | | OK* (2)| 
 ||Pancake sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/pancake_sort.py) | | | AGAIN| 
-||Selection sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/selection_sort.py), [js](https://github.com/yennanliu/CS_basics/blob/master/algorithm/js/selection_sort.js) | | | AGAIN| 
+||Selection sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/selection_sort.py), [JS](https://github.com/yennanliu/CS_basics/blob/master/algorithm/js/selection_sort.js) | | | AGAIN| 
 ||Topological sort| [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/topological_sort.py) | | | AGAIN| 
 ||md5 | [Python](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/md5.py) | | | AGAIN| 
 ||Union Find | [Python union find](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/union_find.py), [Python union find check cyclic](https://github.com/yennanliu/CS_basics/blob/master/algorithm/python/union_find_if_cyclic.py) | | | AGAIN| 

algorithm/js/merge_sort.js

@@ -0,0 +1,42 @@
+//https://repl.it/@aneagoie/mergeSort
+
+function mergeSort (array) {
+  if (array.length === 1) {
+    return array
+  }
+  // Split Array in into right and left
+  const length = array.length;
+  const middle = Math.floor(length / 2)
+  const left = array.slice(0, middle) 
+  const right = array.slice(middle)
+  // console.log('left:', left);
+  // console.log('right:', right);
+
+  
+  return merge(
+    mergeSort(left),
+    mergeSort(right)
+  )
+}
+
+function merge(left, right){
+  const result = [];
+  let leftIndex = 0;
+  let rightIndex = 0;
+  while(leftIndex < left.length && 
+        rightIndex < right.length){
+     if(left[leftIndex] < right[rightIndex]){
+       result.push(left[leftIndex]);
+       leftIndex++;
+     } else{
+       result.push(right[rightIndex]);
+       rightIndex++
+    }
+  }  
+  // console.log(left, right)
+  return result.concat(left.slice(leftIndex)).concat(right.slice(rightIndex));
+}
+
+const numbers = [99, 44, 6, 2, 1, 5, 63, 87, 283, 4, 0];
+const answer = mergeSort(numbers);
+console.log(answer);