A devicechange event is fired on an XRSystem object whenever the availability of immersive XR devices has changed; for example, a VR headset or AR goggles have been connected or disconnected. It's a generic Event with no added properties.

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

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

ondevicechange = (event) => {};

If the use of WebXR has been blocked by an xr-spatial-tracking Permissions Policy, devicechange events will not fire.

A generic Event with no added properties.

Triggered whenever the availability of immersive XR devices has changed. For example, when a VR headset or AR goggles have been connected or disconnected.

You can use this event to, for example, monitor for the availability of a WebXR-compatible device so that you can enable a UI element which the user can use to activate immersive mode. This is shown in the example below.

The example shown here handles the devicechange event by toggling the availability of the "Enter XR" button based on whether or not any immersive devices are currently available.

if (navigator.xr) {
  navigator.xr.addEventListener("devicechange", (event) => {
    navigator.xr.isSessionSupported("immersive-vr").then((immersiveOK) => {
      enableXRButton.disabled = !immersiveOK;
    });
  });
}

When devicechange is received, the handler set up in this code calls the XR method isSessionSupported() to find out if there's a device available that can handle immersive VR presentations. If there is, the button to enter XR mode is enabled; otherwise it's disabled.

You can also use the ondevicechange event handler property to set a single handler for devicechange events:

if (navigator.xr) {
  navigator.xr.ondevicechange = (event) => {
    // …
  };
}