The getJointPose() method of the XRFrame interface returns an XRJointPose object providing the pose of a hand joint (see XRHand) relative to a given base space.

joint

An XRJointSpace specifying the hand joint space for which to obtain an XRJointPose describing the item's position and orientation.

baseSpace

An XRSpace to use as the base or origin for the relative position and orientation.

An XRJointPose object specifying the position and orientation of the hand joint, relative to the XRSpace indicated by baseSpace.

Call getJointPose() with an XRJointSpace and an XRReferenceSpace to get an XRJointPose object.

navigator.xr
  .requestSession({ optionalFeatures: ["hand-tracking"] })
  .then(/* … */);

function renderFrame(session, frame) {
  // …

  for (const inputSource of session.inputSources) {
    if (inputSource.hand) {
      const indexFingerTipJoint = inputSource.hand.get("index-finger-tip");
      frame.getJointPose(indexFingerTipJoint, referenceSpace); // XRJointPose
    }
  }
}

• XRHand
• XRJointSpace
• XRSpace