Gyroscope.z

The z read-only property of the Gyroscope interface returns a double precision integer containing the angular velocity of the device along the its z axis.

If a feature policy blocks use of a feature it is because your code is inconsistent with the policies set on your server. This is not something that would ever be shown to a user. The Feature-Policy HTTP header article contains implementation instructions.

A Number.

The gyroscope is typically read in the reading event callback. In the example below this occurs sixty times a second.

let gyroscope = new Gyroscope({frequency: 60});

gyroscope.addEventListener('reading', e => {
  console.log("Angular velocity along the X-axis " + gyroscope.x);
  console.log("Angular velocity along the Y-axis " + gyroscope.y);
  console.log("Angular velocity along the Z-axis " + gyroscope.z);
});
gyroscope.start();