[Rails] How to display multiple markers on Google Map and display a balloon when clicked



Development environment

・ Ruby: 2.5.7 Rails: 5.2.4 ・ Vagrant: 2.2.7 -VirtualBox: 6.1 ・ OS: macOS Catalina


The following has been implemented.

Slim introduction -Login function implementationGoogle Map display -Calculate latitude and longitude with Gocoding API


1. Edit the controller


def index
  @users = User.all
  gon.users = User.all

2. Edit the view


#map style='height: 500px; width: 500px;'

- google_api = "https://maps.googleapis.com/maps/api/js?key=#{ ENV['GOOGLE_MAP_API'] }&callback=initMap".html_safe
script{ async src=google_api }


  let map;
  let marker = []; //I want to display multiple markers, so I arrange them
  let infoWindow = []; //I want to display multiple balloons, so I arrange them
  let markerData = gon.users; //Assign the instance variable defined by the controller to the variable

  function initMap() {
    geocoder = new google.maps.Geocoder()

    map = new google.maps.Map(document.getElementById('map'), {
      center: { lat: 35.6585, lng: 139.7486 }, //The display is centered around Tokyo Tower
      zoom: 12,

    //Display multiple markers and balloons by iterative processing
    for (var i = 0; i < markerData.length; i++) {
      let id = markerData[i]['id']

      //Calculate the latitude and longitude of each point
      markerLatLng = new google.maps.LatLng({
        lat: markerData[i]['latitude'],
        lng: markerData[i]['longitude']

      //Create markers for each point
      marker[i] = new google.maps.Marker({
        position: markerLatLng,
        map: map

      //Create a balloon for each point
      infoWindow[i] = new google.maps.InfoWindow({
        //Contents of the balloon
        content: markerData[i]['address']

      //Add click event to marker

  //Click the marker to display a balloon
  function markerEvent(i) {
    marker[i].addListener('click', function () {
      infoWindow[i].open(map, marker[i]);

If you want to link the contents of the balloon, describe as follows.


//Variableize each user's ID
let id = markerData[i]['id']

infoWindow[i] = new google.maps.InfoWindow({
  // <a>Create a link with a tag
  content: `<a href='/users/${ id }'>${ markerData[i]['address'] }</a>`


If you do not disable turbolinks, the map will not switch, so be sure to disable it.

How to disable turbolinks

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