Which method of the Geolocation application programming interface (API) should a developer use to get periodic updates of a user's coordinates?

To obtain periodic updates of a user's coordinates using the Geolocation API, a developer should utilize the method that actively watches for changes in the user's location. The correct answer is to use the watchPosition() method.

This method allows developers to retrieve the user's current position and then continuously monitor for any updates or changes to that position. It sets up a listener that triggers a callback function every time the position changes, allowing for real-time tracking. This is particularly useful in applications requiring frequent updates of location, such as navigation apps or location-based services.

In contrast, the getCurrentLocation() method would only retrieve the user's position at a single moment in time, without any ongoing updates. The clearWatch() method is used to stop receiving updates set up by watchPosition(), and toString() does not have any relevance in the context of retrieving location updates; it is simply a method for converting an object to a string representation. Thus, watchPosition() is the appropriate choice for receiving continuous location updates.