Using Closures in Event Listeners

This example creates a map with tappable markers displaying a secret message.

TypeScript

function initMap(): void {
  const map = new google.maps.Map(
    document.getElementById("map") as HTMLElement,
    {
      zoom: 4,
      center: { lat: -25.363882, lng: 131.044922 },
    }
  );

  const bounds: google.maps.LatLngBoundsLiteral = {
    north: -25.363882,
    south: -31.203405,
    east: 131.044922,
    west: 125.244141,
  };

  // Display the area between the location southWest and northEast.
  map.fitBounds(bounds);

  // Add 5 markers to map at random locations.
  // For each of these markers, give them a title with their index, and when
  // they are clicked they should open an infowindow with text from a secret
  // message.
  const secretMessages = ["This", "is", "the", "secret", "message"];
  const lngSpan = bounds.east - bounds.west;
  const latSpan = bounds.north - bounds.south;

  for (let i = 0; i < secretMessages.length; ++i) {
    const marker = new google.maps.Marker({
      position: {
        lat: bounds.south + latSpan * Math.random(),
        lng: bounds.west + lngSpan * Math.random(),
      },
      map: map,
    });
    attachSecretMessage(marker, secretMessages[i]);
  }
}

// Attaches an info window to a marker with the provided message. When the
// marker is clicked, the info window will open with the secret message.
function attachSecretMessage(
  marker: google.maps.Marker,
  secretMessage: string
) {
  const infowindow = new google.maps.InfoWindow({
    content: secretMessage,
  });

  marker.addListener("click", () => {
    infowindow.open(marker.get("map"), marker);
  });
}index.ts

JavaScript

function initMap() {
  const map = new google.maps.Map(document.getElementById("map"), {
    zoom: 4,
    center: { lat: -25.363882, lng: 131.044922 },
  });
  const bounds = {
    north: -25.363882,
    south: -31.203405,
    east: 131.044922,
    west: 125.244141,
  };
  // Display the area between the location southWest and northEast.
  map.fitBounds(bounds);
  // Add 5 markers to map at random locations.
  // For each of these markers, give them a title with their index, and when
  // they are clicked they should open an infowindow with text from a secret
  // message.
  const secretMessages = ["This", "is", "the", "secret", "message"];
  const lngSpan = bounds.east - bounds.west;
  const latSpan = bounds.north - bounds.south;

  for (let i = 0; i < secretMessages.length; ++i) {
    const marker = new google.maps.Marker({
      position: {
        lat: bounds.south + latSpan * Math.random(),
        lng: bounds.west + lngSpan * Math.random(),
      },
      map: map,
    });
    attachSecretMessage(marker, secretMessages[i]);
  }
}

// Attaches an info window to a marker with the provided message. When the
// marker is clicked, the info window will open with the secret message.
function attachSecretMessage(marker, secretMessage) {
  const infowindow = new google.maps.InfoWindow({
    content: secretMessage,
  });
  marker.addListener("click", () => {
    infowindow.open(marker.get("map"), marker);
  });
}
index.js

CSS

/* Always set the map height explicitly to define the size of the div
       * element that contains the map. */
#map {
  height: 100%;
}

/* Optional: Makes the sample page fill the window. */
html,
body {
  height: 100%;
  margin: 0;
  padding: 0;
}
style.css

HTML

<!DOCTYPE html>
<html>
  <head>
    <title>Using Closures in Event Listeners</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>
    <link rel="stylesheet" type="text/css" href="./style.css" />
    <script src="./index.js"></script>
  </head>
  <body>
    <div id="map"></div>

    <!-- Async script executes immediately and must be after any DOM elements used in callback. -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap&libraries=&v=weekly"
      async
    ></script>
  </body>
</html>sample.html

All

<!DOCTYPE html>
<html>
  <head>
    <title>Using Closures in Event Listeners</title>
    <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>
    <style type="text/css">
      /* Always set the map height explicitly to define the size of the div
       * element that contains the map. */
      #map {
        height: 100%;
      }

      /* Optional: Makes the sample page fill the window. */
      html,
      body {
        height: 100%;
        margin: 0;
        padding: 0;
      }
    </style>
    <script>
      function initMap() {
        const map = new google.maps.Map(document.getElementById("map"), {
          zoom: 4,
          center: { lat: -25.363882, lng: 131.044922 },
        });
        const bounds = {
          north: -25.363882,
          south: -31.203405,
          east: 131.044922,
          west: 125.244141,
        };
        // Display the area between the location southWest and northEast.
        map.fitBounds(bounds);
        // Add 5 markers to map at random locations.
        // For each of these markers, give them a title with their index, and when
        // they are clicked they should open an infowindow with text from a secret
        // message.
        const secretMessages = ["This", "is", "the", "secret", "message"];
        const lngSpan = bounds.east - bounds.west;
        const latSpan = bounds.north - bounds.south;

        for (let i = 0; i < secretMessages.length; ++i) {
          const marker = new google.maps.Marker({
            position: {
              lat: bounds.south + latSpan * Math.random(),
              lng: bounds.west + lngSpan * Math.random(),
            },
            map: map,
          });
          attachSecretMessage(marker, secretMessages[i]);
        }
      }

      // Attaches an info window to a marker with the provided message. When the
      // marker is clicked, the info window will open with the secret message.
      function attachSecretMessage(marker, secretMessage) {
        const infowindow = new google.maps.InfoWindow({
          content: secretMessage,
        });
        marker.addListener("click", () => {
          infowindow.open(marker.get("map"), marker);
        });
      }
    </script>
  </head>
  <body>
    <div id="map"></div>

    <!-- Async script executes immediately and must be after any DOM elements used in callback. -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap&libraries=&v=weekly"
      async
    ></script>
  </body>
</html>
inline.html

/* Always set the map height explicitly to define the size of the div * element that contains the map. */ #map { height: 100%; } /* Optional: Makes the sample page fill the window. */ html, body { height: 100%; margin: 0; padding: 0; }

<!DOCTYPE html> <html> <head> <title>Using Closures in Event Listeners</title> <script src="https://polyfill.io/v3/polyfill.min.js?features=default"></script>  </head> <body> <div id="map"></div>  <script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg&callback=initMap&libraries=&v=weekly" async ></script> </body> </html>