Reload Markers on Google's Maps API

Question

Here is my code(most code from Google's API page).

<script>
    var beaches = [
      ['Bondi Beach', -12.890542, 120.274856, 4],
      ['Coogee Beach', -12.923036, 520.259052, 5],
      ['Cronulla Beach', -12.028249, 1221.157507, 3],
      ['Manly Beach', -12.80010128657071, 1121.28747820854187, 2],
      ['Maroubra Beach', -33.950198, 121.259302, 1]
    ];

    function setMarkers(map, locations) {
      for (var i = 0; i < locations.length; i++) {
        var beach = locations[i];
        var myLatLng = new google.maps.LatLng(beach[1], beach[2]);
        var marker = new google.maps.Marker({
            position: myLatLng,
            map: map,
            title: beach[0],
            zIndex: beach[3]
        });
      }
    }

    function initialize() {
      var mapOptions = {
        zoom: 3,
        center: new google.maps.LatLng(38.77417, -9.13417),
        mapTypeId: google.maps.MapTypeId.SATELLITE
      }
      var map = new google.maps.Map(document.getElementById('map-canvas'),
                                    mapOptions);

      setMarkers(map, beaches);
    }

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

    setInterval(function() { setMarkers(map, beaches); }, 5000);

</script>

What I simply want to do is reload only the markers. I tried reloading the map using initialize function but it didn't work. Then I tried to reloading using setMarkers function and still no luck...

Thanks for your help.

Answer 1

Few things you should do / things that I have changed from your original code:

1. Use valid lat/lng coordinates for your markers (1121.28747820854187 for example is not a valid lng)
2. Create a global variable for your map (easier to reference in your script)
3. Create an array to hold your markers
4. I have added a marker animation animation: google.maps.Animation.DROP, to your markers, so that you can see when they are reloaded, and a reload markers button to call the reload function.

Basically what you want to do is:

1. Create each marker within the setMarkers function
2. Push each marker to the markers array
3. When reloading your markers, loop through your markers array and call setMap(null) on each marker to remove it from the map
4. Once done, call setMarkers again to re-draw your markers

Updated code:

let map;
let markers = []; // Create a marker array to hold your markers
const beaches = [
  ['Bondi Beach', 10, 10, 4],
  ['Coogee Beach', 10, 11, 5],
  ['Cronulla Beach', 10, 12, 3],
  ['Manly Beach', 10, 13, 2],
  ['Maroubra Beach', 10, 14, 1]
];

function setMarkers(locations) {

  for (let i = 0; i < locations.length; i++) {
    let beach = locations[i];
    let myLatLng = new google.maps.LatLng(beach[1], beach[2]);
    const marker = new google.maps.Marker({
      position: myLatLng,
      map: map,
      animation: google.maps.Animation.DROP,
      title: beach[0],
      zIndex: beach[3]
    });

    // Push marker to markers array
    markers.push(marker);
  }
}

function reloadMarkers() {

  // Loop through markers and set map to null for each
  for (let i = 0; i < markers.length; i++) {

    markers[i].setMap(null);
  }

  // Reset the markers array
  markers = [];

  // Call set markers to re-add markers
  setMarkers(beaches);
}

async function initMap() {
  // Request libraries when needed, not in the script tag.
  const {
    Map
  } = await google.maps.importLibrary("maps");

  map = new Map(document.getElementById("map-canvas"), {
    zoom: 5,
    center: new google.maps.LatLng(10, 12),
    mapTypeId: google.maps.MapTypeId.SATELLITE
  });
  
  setMarkers(beaches);

  // Bind event listener on button to reload markers
  document.getElementById('reloadMarkers').addEventListener('click', reloadMarkers);
}

initMap();

#map-canvas {
  height: 140px;
}

<div id="map-canvas"></div>
<button id="reloadMarkers">Reload</button>
<script>
  (g=>{var h,a,k,p="The Google Maps JavaScript API",c="google",l="importLibrary",q="__ib__",m=document,b=window;b=b[c]||(b[c]={});var d=b.maps||(b.maps={}),r=new Set,e=new URLSearchParams,u=()=>h||(h=new Promise(async(f,n)=>{await (a=m.createElement("script"));e.set("libraries",[...r]+"");for(k in g)e.set(k.replace(/[A-Z]/g,t=>"_"+t[0].toLowerCase()),g[k]);e.set("callback",c+".maps."+q);a.src=`https://maps.${c}apis.com/maps/api/js?`+e;d[q]=f;a.onerror=()=>h=n(Error(p+" could not load."));a.nonce=m.querySelector("script[nonce]")?.nonce||"";m.head.append(a)}));d[l]?console.warn(p+" only loads once. Ignoring:",g):d[l]=(f,...n)=>r.add(f)&&u().then(()=>d[l](f,...n))})({
    key: "AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk",
    v: "weekly",
    // Use the 'v' parameter to indicate the version to use (weekly, beta, alpha, etc.).
    // Add other bootstrap parameters as needed, using camel case.
  });
</script>

JSFiddle demo

Answer 2

even if initially it s set as invisible after setting new location to Marker:

markerLcl.setPosition(mLatLng)

got it redrawn in the new place by:

        markerLcl.setMap(null)
        markerLcl.setMap(mMap)

Answer 3

This may not be the initial doubt, but to clear the markers and other components of the map, just before loading the map and its components put:

map.clear ();

Answer 4

To reload the markers, when you create then, push them to an array.

Then create a function where you iterate through the array, setting the markers map as null. After this, erase the array.

Edit: I will assume, you gonna return a JSON with the following structure on your PHP

{
  beaches: [
            [
              "Bondi Beach",
              -12.890542,
              120.274856,
              4
            ],
            [
              "Other Beach",
              -12.890542,
              120.274856,
              5
            ]
           ]
}

I'm also assumming you gonna use jQuery (just to simplify the ajax call and json iteration)

<script>
    var arrMarkers = [];

    var beaches = [
      ['Bondi Beach', -12.890542, 120.274856, 4],
      ['Coogee Beach', -12.923036, 520.259052, 5],
      ['Cronulla Beach', -12.028249, 1221.157507, 3],
      ['Manly Beach', -12.80010128657071, 1121.28747820854187, 2],
      ['Maroubra Beach', -33.950198, 121.259302, 1]
    ];

    function setMarkers(map, locations) {
      for (var i = 0; i < locations.length; i++) {
        var beach = locations[i];
        var myLatLng = new google.maps.LatLng(beach[1], beach[2]);
        var marker = new google.maps.Marker({
            position: myLatLng,
            map: map,
            title: beach[0],
            zIndex: beach[3]
        });

        arrMarkers.push(marker);
      }
    }

    function initialize() {
      var mapOptions = {
        zoom: 3,
        center: new google.maps.LatLng(38.77417, -9.13417),
        mapTypeId: google.maps.MapTypeId.SATELLITE
      }
      var map = new google.maps.Map(document.getElementById('map-canvas'),
                                    mapOptions);

      setMarkers(map, beaches);
    }

    function removeMarkers(){
     var i;
     for(i=0;i<arrMarkers.length;i++){
       arrMarkers[i].setMap(null);
     }
     arrMarkers = [];

    }

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

    setInterval(function() { 
       updateTheMarkers();
    }, 5000);

    function updateTheMarkers(){
      $.ajax({
      type: "GET",
      url: "/yourphp.php",
              success: function (data) {
                  //We remove the old markers
                  removeMarkers();
                  var jsonObj = $.parseJSON(data),
                      i;

                  beaches =[];//Erasing the beaches array

                  //Adding the new ones
                  for(i=0;i < jsonObj.beaches.length; i++) {
                    beaches.push(jsonObj.beaches[i]);
                  }

                  //Adding them to the map
                  setMarkers(map, beaches);
              }
         });
    }

</script>

Basically, now, every 5 secs your javascript do an ajax request to your php, your php will return an updated json with the new beaches, you will remove the old markers, fill the array with the new locations and generate the new markers.