Geolocation.watchPosition()

The Geolocation method watchPosition() method is used to register a handler function that will be called automatically each time the position of the device changes. You can also, optionally, specify an error handling callback function.

This method returns a watch ID value that then can be used to unregister the handler by passing it to the Geolocation.clearWatch() method.

Syntax

var id = navigator.geolocation.watchPosition(success[, error[, options]])

Parameters

• success A callback function that takes a GeolocationPosition object as an input parameter.
• error Optional An optional callback function that takes a GeolocationPositionError object as an input parameter.
• options Optional An optional object including the following parameters: maximumAge: Is a positive long value indicating the maximum age in milliseconds of a possible cached position that is acceptable to return. If set to 0, it means that the device cannot use a cached position and must attempt to retrieve the real current position. If set to Infinity the device must return a cached position regardless of its age. Default: 0. timeout: Is a positive long value representing the maximum length of time (in milliseconds) the device is allowed to take in order to return a position. The default value is Infinity, meaning that getCurrentPosition() won't return until the position is available. ** enableHighAccuracy: Is a boolean value that indicates the application would like to receive the best possible results. If true and if the device is able to provide a more accurate position, it will do so. Note that this can result in slower response times or increased power consumption (with a GPS chip on a mobile device for example). On the other hand, if false, the device can take the liberty to save resources by responding more quickly and/or using less power. Default: false.

Return value

An integer ID that identifies the registered handler. The ID can be passed to the Geolocation.clearWatch() to unregister the handler.

Example

var id, target, options;

function success(pos) {

var crd = pos.coords;

if (target.latitude === crd.latitude && target.longitude === crd.longitude) {

console.log('Congratulations, you reached the target');

navigator.geolocation.clearWatch(id);

}

}

function error(err) {

console.warn('ERROR(' + err.code + '): ' + err.message);

}

target = {

latitude : 0,

longitude: 0

};

options = {

enableHighAccuracy: false,

timeout: 5000,

maximumAge: 0

};

id = navigator.geolocation.watchPosition(success, error, options);