The read-only XRInputSource property handedness indicates which of the user's hands the WebXR input source is associated with, or if it's not associated with a hand at all.

A string indicating whether the input controller is held in one of the user's hands, and if it is, which hand. The value is one of the following:

none

The input controller is not associated with one of the user's hands.

left

The input controller is being held in, worn on, or is attached to the user's left hand.

right

The input controller is being held in, worn on, or is attached to the user's right hand.

If the input source is not a device associated with a user's hand (whether by being held, attached, or worn), the value of handedness is none. This may indicate, for example, an input source which isn't hand-held, such as controls built into a headset or an input device attached to the head or body.

One important usage scenario for handedness is to determine which hand a controller is in so you can draw a representation of that hand (or the device that hand is controlling) in virtual space.

function updateInputSources(session, frame, refSpace) {
  for (const source of session.inputSources) {
    if (source.gripSpace) {
      const gripPose = frame.getPose(source.gripSpace, refSpace);

      if (gripPose) {
        myRenderHandObject(gripPose, inputSource.handedness);
      }
    }
  }
}

This function, which would be called every animation frame (or possibly just periodically, depending on the degree of smoothness required and any performance constraints), scans the list of input sources looking for any which have a gripSpace which isn't null. If a gripSpace is present, that means the input source is a hand-held device of some sort, so it should be rendered visibly if possible.

If gripSpace is non-null, the function proceeds to get the pose for the gripSpace transformed into the current reference space. Assuming that's then valid, a function called myRenderHandObject() is called with the grip's pose and the value of handedness. It then draws the appropriate model positioned and formed for the correct hand.

• WebXR Device API
• Inputs and input sources
• Using gamepads in WebXR applications