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The materials presented in this chapter deal with low-level APIs. If you’re using a framework like React or Angular, make sure to check out the chapter on Working with Frameworks.

Dealing with events: standard JS ↔ Maps API Listening to events Triggering events Connecting the map to the DOM Trivial state management Map → DOM DOM → Map Removing artifacts from the map In this chapter →

Google Maps’ true power lies in exposing mouse and keyboard events for us to work with.

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Try dragging and clicking on the map and to see which events get highlighted in blue.

Embed courtesy of Google’s documentation

When you interact with the map canvas or its artifacts (i.e. markers, info windows, or shapes), an event is triggered.

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These events usually inherit from the google.maps.Event class and are divided into two categories:

User-triggered events (click, dblclick, rightclick etc), as defined in the respective Google Maps class: Map Events, Marker Events, Polygon Events, InfoWindow Events etc.

State change events using a property_changed convention → e.g. position_changed, bounds_changed, visible_changed and so on.

Certain traditional DOMEvents can also bubble up from a map artifact — think clicking on some HTML content inside a custom InfoWindow. More on this later.

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Keep in mind that Google Maps doesn’t expose all UI interactions. For instance, clicking on native markers (POI icons) isn’t observable — you cannot listen to the click events. Sometimes it isn’t even desirable! When you place custom markers on top of the native markers and bind them to custom info windows, you don’t want the native info windows to appear… So, to purposefully disable clicking on the native map icons, set clickableIcons: true when initializing your Map.

Dealing with events: standard JS ↔ Maps API

Listening to events

To listen to clicks on a traditional <button id="button"> HTML element, you have multiple options:

Add an onclick attribute in HTML:

<!-- either as an inline function -->
<button id="button" onclick="alert('I was clicked')">

<!-- or as reference to a function -->
<button id="button" onclick="handleBtnClick">

Bind an eventListener in JS:

const btn = document.querySelector("#button");
btn.addEventListener('click',
  (evt) => {
    // handle clicks
  },
);

In Google Maps, you can listen to clicks on a marker two ways:

Either directly on the google.maps.Marker instance (and any MVC instance like google.maps.Polygon, google.maps.Cirlce etc):

marker.addListener("click", () => {
   // handle clicks 
});

Or via the event namespace:

google.maps.event.addListener(marker, "click", () => {
	// handle clicks
});

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These two methods are functionally equivalent and both return a MapsEventListener. We’ll come back to storing event listeners later.

Triggering events

Assuming the same #button element from above, you can programmatically trigger clicks on it in two ways:

button.click()

button.dispatchEvent(new MouseEvent("click"))

In Google Maps, however, there’s only one way — through the event namespace’s trigger:

const marker = new google.maps.Marker({ ... });

google.maps.event.trigger(marker, "click");

which brings us to…

Connecting the map to the DOM

Even if your map is the most prominent element on the page, it will likely not be the only element.

3. Interactivity & Events

Dealing with events: standard JS ↔ Maps API

Listening to events

Triggering events

Connecting the map to the DOM