The XRSystem interface's requestSession() method returns a promise which resolves to an XRSession object through which you can manage the requested type of WebXR session.

While only one immersive VR session can be active at a time, multiple inline sessions can be in progress at once.

mode

A String defining the XR session mode. The supported modes are:

• Experimental immersive-ar: The session's output will be given exclusive access to the immersive device, but the rendered content will be blended with the real-world environment. The session's environmentBlendMode indicates the method to be used to blend the content together.
• immersive-vr: Indicates that the rendered session will be displayed using an immersive XR device in VR mode; it is not intended to be overlaid or integrated into the surrounding environment. The environmentBlendMode is expected to be opaque if possible, but might be additive if the hardware requires it.
• inline: The output is presented inline within the context of an element in a standard HTML document, rather than occupying the full visual space. Inline sessions can be presented in either mono or stereo mode, and may or may not have viewer tracking available. Inline sessions don't require special hardware and should be available on any user agent offering WebXR API support.

options Optional

An object to configure the XRSession. If none are included, the device will use a default feature configuration for all options.

• requiredFeatures Optional: An array of values which the returned XRSession must support. See Session features below.
• optionalFeatures Optional: An array of values identifying features which the returned XRSession may optionally support. See Session features below.
• domOverlay Optional: An object with a required root property that specifies the overlay element that will be displayed to the user as the content of the DOM overlay. See the example below.
• depthSensing Optional: An object with two required properties usagePreference and dataFormatPreference to configure how to perform depth sensing. See the example below.

A Promise that resolves with an XRSession object if the device and user agent support the requested mode and features.

This method doesn't throw true exceptions; instead, it rejects the returned promise, passing into it a DOMException whose name is one of the following:

InvalidStateError DOMException

Returned if the requested session mode is immersive-vr but there is already an immersive VR session either currently active or in the process of being set up. There can only be one immersive VR session at a time.

NotSupportedError DOMException

Returned if there is no WebXR-compatible device available, or the device does not support the specified sessionMode; this can also be thrown if any of the required options are unsupported.

SecurityError DOMException

Returned if permission to enter the specified XR mode is denied. This can happen for several reasons, which are covered in more detail in Permissions and security.

The following session features and reference spaces can be requested, either as optionalFeatures or requiredFeatures.

anchors

Enable use of XRAnchor objects.

bounded-floor

Similar to the local type, except the user is not expected to move outside a predetermined boundary, given by the boundsGeometry in the returned object.

depth-sensing

Enable the ability to obtain depth information using XRDepthInformation objects.

dom-overlay

Enable allowing to specify a DOM overlay element that will be displayed to the user.

hand-tracking

Enable articulated hand pose information from hand-based input controllers (see XRHand and XRInputSource.hand).

hit-test

Enable hit testing features for performing hit tests against real-world geometry.

layers

Enable the ability to create various layer types (other than XRProjectionLayer).

light-estimation

Enable the ability to estimate environmental lighting conditions using XRLightEstimate objects.

local

Enable a tracking space whose native origin is located near the viewer's position at the time the session was created. The exact position depends on the underlying platform and implementation. The user isn't expected to move much if at all beyond their starting position, and tracking is optimized for this use case.

local-floor

Similar to the local type, except the starting position is placed in a safe location for the viewer to stand, where the value of the y axis is 0 at floor level. If that floor level isn't known, the user agent will estimate the floor level. If the estimated floor level is non-zero, the browser is expected to round it such a way as to avoid fingerprinting (likely to the nearest centimeter).

secondary-views

Enable XRView objects to be secondary views. This can be used for first-person observer views used for video capture, or "quad views" where there are two views per eye, with differing resolution and fields of view.

unbounded

Enable a tracking space which allows the user total freedom of movement, possibly over extremely long distances from their origin point. The viewer isn't tracked at all; tracking is optimized for stability around the user's current position, so the native origin may drift as needed to accommodate that need.

viewer

Enable a tracking space whose native origin tracks the viewer's position and orientation.

Several session features and the various reference spaces have minimum security and privacy requirements, like asking for user consent and/or requiring the Permissions-Policy: xr-spatial-tracking directive to be set. See also Permissions and security for more details.

See also transient user activation.

The following example calls requestSession() requesting an "immersive-vr" session. If the Promise resolves, it sets up a session and initiates the animation loop.

navigator.xr
  .requestSession("immersive-vr")
  .then((xrSession) => {
    xrSession.addEventListener("end", onXRSessionEnded);
    // Do necessary session setup here.
    // Begin the session's animation loop.
    xrSession.requestAnimationFrame(onXRAnimationFrame);
  })
  .catch((error) => {
    // "immersive-vr" sessions are not supported
    console.error(
      "'immersive-vr' isn't supported, or an error occurred activating VR!",
    );
  });

The following example shows how to use both isSessionSupported() and requestSession(). First, it checks to see if WebXR is available by verifying the existence of navigator.xr. Next, it calls isSessionSupported(), passing it the desired session option before enabling controls for entering XR. Adding controls is a necessary step because entering XR requires a user action. Finally, the onButtonClicked() method calls requestSession() using the same session option passed to isSessionSupported().

if (navigator.xr) {
  navigator.xr.isSessionSupported("immersive-vr").then((isSupported) => {
    if (isSupported) {
      immersiveButton.addEventListener("click", onButtonClicked);
      immersiveButton.textContent = "Enter XR";
      immersiveButton.disabled = false;
    } else {
      console.error("WebXR doesn't support immersive-vr mode!");
    }
  });
} else {
  console.error("WebXR is not available!");
}

function onButtonClicked() {
  if (!xrSession) {
    navigator.xr.requestSession("immersive-vr").then((session) => {
      xrSession = session;
      // onSessionStarted() not shown for reasons of brevity and clarity.
      onSessionStarted(xrSession);
    });
  } else {
    // Button is a toggle button.
    xrSession.end().then(() => (xrSession = null));
  }
}

Require an unbounded experience in which the user is able to freely move around their physical environment:

navigator.xr.requestSession("immersive-vr", {
  requiredFeatures: ["unbounded"],
});

Here, the caller is able to handle both CPU- and GPU-optimized usage, as well as both "luminance-alpha" and "float32" formats. The order indicates preference for CPU and "luminance-alpha":

navigator.xr.requestSession("immersive-ar", {
  requiredFeatures: ["depth-sensing"],
  depthSensing: {
    usagePreference: ["cpu-optimized", "gpu-optimized"],
    formatPreference: ["luminance-alpha", "float32"],
  },
});