Geolocation API

You will often want to retrieve a user's location information in your web app, for example to plot their location on a map, or display personalized information relevant to their location.

The Geolocation API is accessed via a call to navigator.geolocation; this will cause the user's browser to ask them for permission to access their location data. If they accept, then the browser will use the best available functionality on the device to access this information (for example, GPS).

The developer can now access this location information in a couple of different ways:

• Geolocation.getCurrentPosition(): Retrieves the device's current location.
• Geolocation.watchPosition(): Registers a handler function that will be called automatically each time the position of the device changes, returning the updated location.

In both cases, the method call takes up to three arguments:

• A mandatory success callback: If the location retrieval is successful, the callback executes with a GeolocationPosition object as its only parameter, providing access to the location data.
• An optional error callback: If the location retrieval is unsuccessful, the callback executes with a GeolocationPositionError object as its only parameter, providing access information on what went wrong.
• An optional object which provides options for retrieval of the position data.

For further information on Geolocation usage, read Using the Geolocation API.

Geolocation

The main class of this API — contains methods to retrieve the user's current position, watch for changes in their position, and clear a previously-set watch.

GeolocationPosition

Represents the position of a user. A GeolocationPosition instance is returned by a successful call to one of the methods contained inside Geolocation, inside a success callback, and contains a timestamp plus a GeolocationCoordinates object instance.

GeolocationCoordinates

Represents the coordinates of a user's position; a GeolocationCoordinates instance contains latitude, longitude, and other important related information.

GeolocationPositionError

A GeolocationPositionError is returned by an unsuccessful call to one of the methods contained inside Geolocation, inside an error callback, and contains an error code and message.

Navigator.geolocation

The entry point into the API. Returns a Geolocation object instance, from which all other functionality can be accessed.

See Using the Geolocation API for example code.

As Wi-Fi-based locating is often provided by Google, the vanilla Geolocation API may be unavailable in China. You may use local third-party providers such as Baidu, Autonavi, or Tencent. These services use the user's IP address and/or a local app to provide enhanced positioning.

• Using the Geolocation API
• Geolocation API on w3.org
• Who moved my geolocation? (Hacks blog)