Element: fullscreenchange event

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

onfullscreenchange = (event) => { }

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

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

const el = document.getElementById("fullscreen-div");

el.addEventListener("fullscreenchange", fullscreenchangeHandler);
// or
el.onfullscreenchange = fullscreenchangeHandler;

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