Today we create a ‘Type Ahead’ feature. When you type something in the search bar, it will show all the matched states/cities with the corresponding population.

The data is coming in from an external json file from a URL. The data (which is a huge array) needs to be fetched and when someone types in the search box, it will show a subset of the cities/states.

In this task we learn about AJAX (Asynchronous JavaScript and XML). It is a web development technique used to communicate with a server, without reloading the page.

The data is fetched using the browser’s Fetch API, which is an interface for fetching resources. According to Mozilla’s MDN. The method takes one mandatory argument, the path to the resource you want to fetch. It returns a Promise, which is an obejct used to handle asynchronous operations in JS.

I enjoyed this excercise!

Repo here and demo is here.

JS code snippet below:

const endpoint = '';

const cities = [];

// fetch api from the browser is used, and it returns a promise object
  .then(blob => blob.json())
  // Spread into the push method and that will give us the cities array we need
  .then(data => cities.push(;

function findMatches(wordToMatch, cities) {
  // find subset of the array required
  return cities.filter(place => {
    // this is where we check if the city or state matches what was searched
    const regex = new RegExp(wordToMatch, 'gi'); // Flags: g = global, i = insensitive
    return || place.state.match(regex);

// puts in commas
function numberWithCommas(x) {
  return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');

// When we type into the search box, it should call this method, and then call findMatches
// to find the cities/states that match the input in the box
function displayMatches() {
  // displays filtered array to the list
  const matchArray = findMatches(this.value, cities);
  const html = => {
    const regex = new RegExp(this.value, 'gi');
    const cityName =, `<span class="hl">${this.value}</span>`);
    const stateName = place.state.replace(regex, `<span class="hl">${this.value}</span>`);
    return `
        <span class="name">${cityName}, ${stateName}</span>
        <span class="population">${numberWithCommas(place.population)}</span>
  suggestions.innerHTML = html;

// select the search bar and the suggestions list
const searchInput = document.querySelector('.search');
const suggestions = document.querySelector('.suggestions');

searchInput.addEventListener('change', displayMatches);
searchInput.addEventListener('keyup', displayMatches);