implemented Binary search algorithm

Author: mehediislamripon

Diff for: README.md

@@ -28,4 +28,5 @@
 | Problem - 24  | Find your crushes phone number  |
 | Problem - 25  | Plus One - 66.LeetCode - Easy  |
 | Problem - 26  | Linear Search implementation with JS  |
+| Problem - 27  | Binary Search implementation with JS  |
 <!-- | Problem - 22  |   | -->

Diff for: problem-27.js

@@ -0,0 +1,20 @@
+// binary search implementation
+const arr = [1, 3, 5, 7, 8, 9];
+
+const binarySearch = (arr, x, start = 0, end = arr.length) => {
+   // If the item does not exist, return -1
+   if (end < start) return -1;
+
+   // Calculate middle index of the array
+   let mid = Math.floor((start + end) / 2);
+
+   // Is the middle a match?
+   if (arr[mid] === x) return mid;
+
+   // Is the middle less than x
+   if (arr[mid] < x) return binarySearch(arr, x, mid + 1, end);
+   // Else the middle is more than x
+   else return binarySearch(arr, x, start, mid - 1);
+};
+
+console.log(binarySearch(arr, 9));