Find the Index of the First Occurence in a String

A LeetCode's Algorithm

Given two strings needle and haystack,
return the index of the first occurrence of needle in haystack,
or -1 if needle is not part of haystack.

javascript/strStr.js

@@ -0,0 +1,19 @@
+/**
+ * Visit https://leetcode.com/problems/find-the-index-of-the-first-occurrence-in-a-string/description/
+ * for full problem description
+ * 
+ * Given two strings needle and haystack, 
+ * return the index of the first occurrence of needle in haystack, 
+ * or -1 if needle is not part of haystack.
+ * 
+ * @param {string} haystack
+ * @param {string} needle
+ * @return {number}
+ */
+var strStr = function (haystack, needle) {
+    // The JavaScript in-built string search method indexOf
+    // returns the index of the first occurrence of needle in haystack,
+    // or -1 if needle is not part of haystack, and is all that is needed
+    // to write the algorithm that solves this problem.
+    return haystack.indexOf(needle);
+};