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>
    <script
      src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap&libraries=&v=weekly"
      defer
    ></script>
    <link rel="stylesheet" type="text/css" href="./style.css" />
    <script src="./index.js"></script>
  </head>
  <body>
    <div id="map"></div>
  </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>
    <script
      src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap&libraries=&v=weekly"
      defer
    ></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>
  </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> <script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyBIwzALxUPNbatRBj3Xi1Uhp0fFzwWNBkE&callback=initMap&libraries=&v=weekly" defer ></script>  </head> <body> <div id="map"></div> </body> </html>

Create a starter application from sample

A skeleton starter application using TypeScript, Webpack, and Babel can be generated from this sample using one of the methods below.

Run Locally

Node.js is required to run this sample locally. Follow these instructions to install Node.js and NPM.

npx @googlemaps/js-samples init event-closure DESTINATION_FOLDER

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