Google map API v3 - Add multiple infowindows

Question

I've got a working section of google maps javascript, I did have a problem.

Now the issue I had was that only one infowindow was showing up, the last. I found a solution on another stack thread that worked out. But I couldn't really work out why. I'm fairly new to Javascript so I was hoping someone could explain to me what changed and how.

Here is the working code:

function setMarkers(map, locations){
  for(var i = 0; i < locations.length; i++){
    var marker = locations[i];
    var latLng = new google.maps.LatLng(locations[i][1], locations[i][2]);
    var content = locations[i][0];
    var infowindow = new google.maps.InfoWindow();

    marker = new google.maps.Marker({
      position:latLng,
      map: map
    });

    google.maps.event.addListener(marker, 'click', function(content){
      return function(){
        infowindow.setContent(content);
        infowindow.open(map, this);
      }
    }(content));
  }
}

Here is the original broken code was (I'll paste only that which changed):

 google.maps.event.addListener(marker, 'click', function(){
      infowindow.setContent(content);
      infowindow.open(map, marker);
    });

Now what I'd like to know if you'd be so kind, is:

1. what function does the return fn serve, and

2. what does the added (content) at the end of addListener (}(content));) do since as far as I can see the content has already been set within the setContent property.

Thank-you!

Answer 1

Don't loop your infowindow...
You need only one instance of the infowindow object.
Move it outside of the loop, same for your functions.
Inside the loop assign its content as relative to the clicked marker

const locations = [
  {lat: 45.840196, lng: 15.964331, name: "Zagreb"},
  {lat: 43.514851, lng: 16.449083, name: "Split"},
  {lat: 42.645725, lng: 18.094058, name: "Dubrovnik"},
];

function initGoogleMap(){

  const infowindow = new google.maps.InfoWindow(); // Only one InfoWindow
  const map = new google.maps.Map(document.getElementById('map-canvas'), {
      zoom: 6,
      center: new google.maps.LatLng(45, 15)
  });
  
  function placeMarker( loc ) {
    const marker = new google.maps.Marker({
      position : new google.maps.LatLng( loc.lat, loc.lng ),
      map : map
    });
    google.maps.event.addListener(marker, 'click', function(){
        infowindow.close(); // Close previously opened infowindow
        infowindow.setContent(`<div id="infowindow">${loc.name}</div>`);
        infowindow.open(map, marker);
    });
  }
  
  // ITERATE ALL LOCATIONS. Pass every location to placeMarker
  locations.forEach( placeMarker );
  
}

google.maps.event.addDomListener(window, 'load', initGoogleMap);

html, body, #map-canvas { height: 100%; margin: 0px; }
#infowindow{ padding: 10px; }

<script src="https://maps.googleapis.com/maps/api/js?v=3.exp"></script>
<div id="map-canvas"></div>