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Using Closures in Event Listeners

  • This example demonstrates creating a Google Map with 5 randomly placed markers within a defined boundary in Australia.

  • Each marker, when clicked, reveals a part of a secret message using an info window.

  • The code is provided in both TypeScript and JavaScript, utilizing the Google Maps JavaScript API.

  • The sample can be run locally with Git and Node.js or tried online using JSFiddle or Google Cloud Shell.

  • CSS is included to ensure the map fills the browser window and has an explicit height.

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

Read thedocumentation.

TypeScript

asyncfunctioninitMap(){// Request needed libraries.const{Map}=awaitgoogle.maps.importLibrary("maps")asgoogle.maps.MapsLibrary;const{AdvancedMarkerElement}=awaitgoogle.maps.importLibrary("marker")asgoogle.maps.MarkerLibrary;constmap=newgoogle.maps.Map(document.getElementById("map")asHTMLElement,{zoom:4,center:{lat:-25.363882,lng:131.044922},mapId:"DEMO_MAP_ID",});constbounds: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.constsecretMessages=["This","is","the","secret","message"];constlngSpan=bounds.east-bounds.west;constlatSpan=bounds.north-bounds.south;for(leti=0;i <secretMessages.length;++i){constmarker=newgoogle.maps.marker.AdvancedMarkerElement({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.functionattachSecretMessage(marker:google.maps.marker.AdvancedMarkerElement,secretMessage:string){constinfowindow=newgoogle.maps.InfoWindow({content:secretMessage,});marker.addListener("click",()=>{infowindow.open(marker.map,marker);});}initMap();
Note: Read theguide on using TypeScript and Google Maps.

JavaScript

asyncfunctioninitMap(){// Request needed libraries.const{Map}=awaitgoogle.maps.importLibrary("maps");const{AdvancedMarkerElement}=awaitgoogle.maps.importLibrary("marker");constmap=newgoogle.maps.Map(document.getElementById("map"),{zoom:4,center:{lat:-25.363882,lng:131.044922},mapId:"DEMO_MAP_ID",});constbounds={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.constsecretMessages=["This","is","the","secret","message"];constlngSpan=bounds.east-bounds.west;constlatSpan=bounds.north-bounds.south;for(leti=0;i <secretMessages.length;++i){constmarker=newgoogle.maps.marker.AdvancedMarkerElement({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.functionattachSecretMessage(marker,secretMessage){constinfowindow=newgoogle.maps.InfoWindow({content:secretMessage,});marker.addListener("click",()=>{infowindow.open(marker.map,marker);});}initMap();
Note: The JavaScript is compiled from the TypeScript snippet.

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;}

HTML

<html>  <head>    <title>Using Closures in Event Listeners</title>    <link rel="stylesheet" type="text/css" href="./style.css" />    <script type="module" src="./index.js"></script>  </head>  <body>    <div></div>    <!-- prettier-ignore -->    <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: "AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg", v: "weekly"});</script>  </body></html>

Try Sample

Clone Sample

Git and Node.js are required to run this sample locally. Follow theseinstructions to install Node.js and NPM. The following commands clone, install dependencies and start the sample application.

gitclone-bsample-event-closurehttps://github.com/googlemaps/js-samples.gitcdjs-samplesnpminpmstart

Other samples can be tried by switching to any branch beginning withsample-SAMPLE_NAME.

gitcheckoutsample-SAMPLE_NAMEnpminpmstart

Except as otherwise noted, the content of this page is licensed under theCreative Commons Attribution 4.0 License, and code samples are licensed under theApache 2.0 License. For details, see theGoogle Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2025-11-21 UTC.