Listening to Events

  • This example demonstrates creating a user-editable, draggable rectangle on a Google Map.

  • An info window dynamically displays the updated coordinates of the rectangle's northeast and southwest corners as the user adjusts it.

  • The sample code utilizes the Google Maps JavaScript API with event listeners and the Rectangle class to achieve this functionality.

  • You can interact with a live version of this example via JSFiddle or Google Cloud Shell, or clone and run the sample locally using Git and Node.js.

This example adds a user-editable rectangle to the map. When the user changes the bounds of the rectangle, an info window pops up displaying the new bounds.

Read the documentation.

TypeScript

// This example adds a user-editable rectangle to the map.
// When the user changes the bounds of the rectangle,
// an info window pops up displaying the new bounds.

let rectangle: google.maps.Rectangle;
let innerMap: google.maps.Map;

let infoWindow: google.maps.InfoWindow;

async function init(): Promise<void> {
    const { Rectangle, InfoWindow } = await google.maps.importLibrary('maps');

    const mapElement = document.querySelector('gmp-map')!;
    innerMap = mapElement.innerMap;

    const bounds = {
        north: 44.599,
        south: 44.49,
        east: -78.443,
        west: -78.649,
    };

    // Define the rectangle and set its editable property to true.
    rectangle = new Rectangle({
        bounds,
        editable: true,
        draggable: true,
    });

    rectangle.setMap(innerMap);

    // Add an event listener on the rectangle.
    rectangle.addListener('bounds_changed', showNewRect);

    // Define an info window on the map.
    infoWindow = new InfoWindow();
}

/** Show the new coordinates for the rectangle in an info window. */
function showNewRect() {
    const ne = rectangle.getBounds()!.getNorthEast();
    const sw = rectangle.getBounds()!.getSouthWest();

    const contentString =
        '<b>Rectangle moved.</b><br>' +
        'New north-east corner: ' +
        ne.lat() +
        ', ' +
        ne.lng() +
        '<br>' +
        'New south-west corner: ' +
        sw.lat() +
        ', ' +
        sw.lng();

    // Set the info window's content and position.
    infoWindow.setContent(contentString);
    infoWindow.setPosition(ne);

    infoWindow.open(innerMap);
}

void init();

JavaScript

// This example adds a user-editable rectangle to the map.
// When the user changes the bounds of the rectangle,
// an info window pops up displaying the new bounds.

let rectangle;
let innerMap;

let infoWindow;

async function init() {
    const { Rectangle, InfoWindow } = await google.maps.importLibrary('maps');

    const mapElement = document.querySelector('gmp-map');
    innerMap = mapElement.innerMap;

    const bounds = {
        north: 44.599,
        south: 44.49,
        east: -78.443,
        west: -78.649,
    };

    // Define the rectangle and set its editable property to true.
    rectangle = new Rectangle({
        bounds,
        editable: true,
        draggable: true,
    });

    rectangle.setMap(innerMap);

    // Add an event listener on the rectangle.
    rectangle.addListener('bounds_changed', showNewRect);

    // Define an info window on the map.
    infoWindow = new InfoWindow();
}

/** Show the new coordinates for the rectangle in an info window. */
function showNewRect() {
    const ne = rectangle.getBounds().getNorthEast();
    const sw = rectangle.getBounds().getSouthWest();

    const contentString =
        '<b>Rectangle moved.</b><br>' +
        'New north-east corner: ' +
        ne.lat() +
        ', ' +
        ne.lng() +
        '<br>' +
        'New south-west corner: ' +
        sw.lat() +
        ', ' +
        sw.lng();

    // Set the info window's content and position.
    infoWindow.setContent(contentString);
    infoWindow.setPosition(ne);

    infoWindow.open(innerMap);
}

void init();

CSS

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

HTML

<html>
    <head>
        <title>Listening to Events</title>

        <link rel="stylesheet" type="text/css" href="./style.css" />
        <script type="module" src="./index.js"></script>
        <script>
            // prettier-ignore
            (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: "GOOGLE_MAPS_API_KEY"
            });
        </script>
    </head>
    <body>
        <gmp-map
            center="44.5452,-78.5389"
            zoom="9"
            map-id="DEMO_MAP_ID"></gmp-map>
    </body>
</html>

Clone Sample

Git and Node.js are required to run this sample locally. Follow these instructions to install Node.js and NPM. You will also need a Google Maps API key.

The following commands clone the repository, install dependencies, and copy the environment file. 

  git clone https://github.com/googlemaps-samples/js-api-samples.git
  cd js-api-samples
  npm i
  cp .env.template .env

Once you copy the environment file, make sure to open the .env file and replace <Insert your own development API key here> with your actual API key before starting the sample. 

  cd samples/rectangle-event
  npm start