add binary search in js (#31)

searching/README.md

@@ -15,6 +15,7 @@
 ### JavaScript
 
 1. [Linear Search](js/linear-search.js)
+2. [Binary Search](js/binary-search.js)
 
 ### Java
 

searching/js/binary-search.js

@@ -0,0 +1,24 @@
+function binarySearch(value, list) {
+    let first = 0;    //left endpoint
+    let last = list.length - 1;   //right endpoint
+    let position = -1;  // After looping if the search item is not found, we will return -1
+    let found = false;  // When item is found we set its value to true
+    let middle;
+ 
+    while (found === false && first <= last) {
+        middle = Math.floor((first + last)/2);
+        if (list[middle] == value) { // If the element is present at the middle itself
+            found = true;
+            position = middle;
+        } else if (list[middle] > value) {  //if in lower half
+            last = middle - 1;
+        } else {  //in in upper half
+            first = middle + 1;
+        }
+    }
+    return position;
+}
+
+console.log(binarySearch(6,[2, 6, 8]));         //expected output = 1
+console.log(binarySearch(10,[2, 3, 10, 14]));   //expected output = 2
+console.log(binarySearch(1,[2, 6, 8]));         //expected output = -1