Magnetometer.y

The y read-only property of the Magnetometer interface returns a double precision integer containing the magnetic field around the device's y axis.

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A Number.

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

let magSensor = new Magnetometer({frequency: 60});

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