28-Haystack.js

//problem link: https://leetcode.com/problems/find-the-index-of-the-first-occurrence-in-a-string/
/**
 * @param {string} haystack
 * @param {string} needle
 * @return {number}
 */
var strStr = function (haystack, needle) {
  for (let i = 0; i < haystack.length - needle.length + 1; i++) {
    if (haystack.substr(i, needle.length) === needle) {
      return i;
    }
  }
  return -1;
};
console.log(strStr("sadbutsad", "sad"));