script.js

const endpoint = 'https://gist.githubusercontent.com/Miserlou/c5cd8364bf9b2420bb29/raw/2bf258763cdddd704f8ffd3ea9a3e81d25e2c6f6/cities.json'

const cities = []

window.fetch(endpoint)
  .then(response => response.json())
  .then(data => cities.push(...data))

function findMatches (wordToMatch, cities) {
  return cities.filter(place => {
    const regex = new RegExp(wordToMatch, '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 matchArr = findMatches(this.value, cities)
  const regex = new RegExp(this.value, 'gi')

  const html = matchArr.map(place => {
    const cityName = place.city.replace(regex, `<span class="hl">${this.value}</span>`)
    const stateName = place.state.replace(regex, `<span class="hl">${this.value}</span>`)

    return `
      <li>
        <span class="name">${cityName}, ${stateName}</span>
        <span class="population">${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)