dsa problem added using javascript for binary search (#338)

JavaScript/binary_search.js

@@ -0,0 +1,28 @@
+function binarySearch(arr, key) {
+  let start = 0;
+  let end = arr.length - 1;
+
+  while (start <= end) {
+    let mid = Math.floor(start + (end - start) / 2);
+
+    if (arr[mid] === key) {
+      return mid;
+    } else if (arr[mid] > key) {
+      end = mid - 1;
+    } else {
+      start = mid + 1;
+    }
+  }
+
+  return -1;
+}
+
+const arr = [2, 3, 4, 10, 40];
+const key = 10;
+
+const result = binarySearch(arr, key);
+if (result !== -1) {
+  console.log("Element found at index:", result);
+} else {
+  console.log("Element not found");
+}