The fullscreenchange event is fired immediately after the browser switches into or out of fullscreen mode.

The event is sent to the Element that is transitioning into or out of fullscreen mode, and this event then bubbles up to the Document.

To find out whether the Element is entering or exiting fullscreen mode, check the value of Document.fullscreenElement: if this value is null then the element is exiting fullscreen mode, otherwise it is entering fullscreen mode.

This event is not cancelable.

Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("fullscreenchange", (event) => {});

onfullscreenchange = (event) => {};

A generic Event.

In this example, a handler for the fullscreenchange event is added to the Document.

If the user clicks on the "Toggle Fullscreen Mode" button, the click handler will toggle fullscreen mode for the div. If document.fullscreenElement has a value it will exit fullscreen mode. If not, the div will be placed into fullscreen mode.

Remember that by the time the fullscreenchange event is handled, the status of the element has already changed. So if the change is to fullscreen mode, document.fullscreenElement will point to the element that is now in fullscreen mode. On the other hand, if document.fullscreenElement is null, fullscreen mode has been canceled.

What that means to the example code is that, if an element is currently in fullscreen mode, the fullscreenchange handler logs the id of the fullscreen element to the console. If document.fullscreenElement is null, the code logs a message that the change is to leave fullscreen mode.

HTML

<h1>fullscreenchange event example</h1>
<div id="fullscreen-div">
  <button id="toggle-fullscreen">Toggle Fullscreen Mode</button>
  <pre id="logger"></pre>
</div>

CSS

* {
  box-sizing: border-box;
}

#fullscreen-div {
  height: 150px;
  padding: 1rem;
  background-color: pink;
}

#logger {
  height: 80px;
  padding: 0 0.5rem;
  background-color: white;
  overflow: scroll;
}

JavaScript

const logger = document.querySelector("#logger");
const fullScreenElement = document.querySelector("#fullscreen-div");

function log(message) {
  logger.textContent = `${logger.textContent}\n${message}`;
}

function fullscreenchanged(event) {
  // document.fullscreenElement will point to the element that
  // is in fullscreen mode if there is one. If there isn't one,
  // the value of the property is null.
  if (document.fullscreenElement) {
    log(`Element: ${document.fullscreenElement.id} entered fullscreen mode.`);
  } else {
    log("Leaving fullscreen mode.");
  }
}

document.addEventListener("fullscreenchange", fullscreenchanged);

// When the toggle button is clicked, enter/exit fullscreen
document.getElementById("toggle-fullscreen").addEventListener("click", () => {
  if (document.fullscreenElement) {
    // exitFullscreen is only available on the Document object.
    document.exitFullscreen();
  } else {
    fullScreenElement.requestFullscreen();
  }
});

• fullscreenerror
• Element: fullscreenchange event
• Fullscreen API
• Guide to the Fullscreen API