What I learned on this mini-project.

This is a property of the window object, that contains data about the users location. You must enable access for it to work.

navigator.geolocation.watchPosition(data => {
    console.log(data);

    speed.textContent = data.coords.speed;
    arrow.style.transform = `rotate(${data.coords.heading}deg)`;
}, (error) => {
    console.error(error);
    alert('ENABLE GEOLOCATION!!!');
});

The geolocation object is only briefly introduced.

This method, allows you to update the users position at regular intervals, instead of getting a snapshot of where they are.

The data returned then needs to be manipulated via a promise, that handles success and failure outcomes.

Most of the data that you will need is contained in this object. Examples of this include the latitude, longitude and heading (representing degrees from north).