This code was taken from JavaScript30 by Wes Bos. This funcionality is common in applications so its handy to have as a code snippet!
//Get all cities in an array from a json file const endpoint = 'https://gist.githubusercontent.com/Miserlou/c5cd8364bf9b2420bb29/raw/2bf258763cdddd704f8ffd3ea9a3e81d25e2c6f6/cities.json'; const cities = []; fetch(endpoint) .then(blob => blob.json()) .then(data => cities.push(...data)); //Filter the one we want based on a regex function findMatches(matchedWord, cities) { return cities.filter(place => { //check what city or state matches const regex = new RegExp(matchedWord, 'gi'); return place.city.match(regex) || place.state.match(regex) }); } function numberWithCommas(x) { return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ","); } function displayMatches() { const searchPhrase = this.value; const matchArray = findMatches(searchPhrase, cities); const html = matchArray.map(place => { const regexHi = new RegExp(this.value, 'gi'); const cityName = place.city.replace(regexHi, `<span class="hl">${this.value}</span>`); const cityState = place.state.replace(regexHi, `<span class="hl">${this.value}</span>`); return `<li> <span class="name">${cityName}, ${cityState}</span> <span class="population">${numberWithCommas(place.population)}</span> </li>`; }).join(''); suggestions.innerHTML = html; } const searchInput = document.querySelector('.search'); const suggestions = document.querySelector('.suggestions'); searchInput.addEventListener('change', displayMatches); searchInput.addEventListener('keyup', displayMatches);