addded solution for binary search

Author: Codeprinz-1

binarySearch.js

@@ -1 +1,13 @@
 // Task: write a function which accepts a sorted array and a value and returns the index at which the value exists. Otherwise, return -1.
+
+const binarySearch = (arr, elem) => {
+  var start = 0;
+  var end = arr.length - 1;
+  var middle = Math.floor((start + end) / 2);
+  while (arr[middle] !== elem && start <= end) {
+    if (elem < arr[middle]) end = middle - 1;
+    else start = middle + 1;
+    middle = Math.floor((start + end) / 2);
+  }
+  return arr[middle] === elem ? middle : -1;
+};