The Geolocation API is used to retrieve the user's location, so that it can for example be used to display their position using a mapping API. This article explains the basics of how to use it.

The geolocation object

TheGeolocation API is available through thenavigator.geolocation object.

If the object exists, geolocation services are available. You can test for the presence of geolocation thusly:

if ("geolocation" in navigator) {  /* geolocation is available */} else {  /* geolocation IS NOT available */}

Getting the current position

To obtain the user's current location, you can call thegetCurrentPosition() method. This initiates an asynchronous request to detect the user's position, and queries the positioning hardware to get up-to-date information. When the position is determined, the defined callback function is executed. You can optionally provide a second callback function to be executed if an error occurs. A third, optional, parameter is an options object where you can set the maximum age of the position returned, the time to wait for a request, and if you want high accuracy for the position.

navigator.geolocation.getCurrentPosition((position) => {  doSomething(position.coords.latitude, position.coords.longitude);});

The above example will cause thedoSomething() function to execute when the location is obtained.

Watching the current position

If the position data changes (either by device movement or if more accurate geo information arrives), you can set up a callback function that is called with that updated position information. This is done using thewatchPosition() function, which has the same input parameters asgetCurrentPosition(). The callback function is called multiple times, allowing the browser to either update your location as you move, or provide a more accurate location as different techniques are used to geolocate you. The error callback function, which is optional just as it is forgetCurrentPosition(), can be called repeatedly.

const watchID = navigator.geolocation.watchPosition((position) => {  doSomething(position.coords.latitude, position.coords.longitude);});

ThewatchPosition() method returns an ID number that can be used to uniquely identify the requested position watcher; you use this value in tandem with theclearWatch() method to stop watching the user's location.

navigator.geolocation.clearWatch(watchID);

Fine tuning the response

BothgetCurrentPosition() andwatchPosition() accept a success callback, an optional error callback, and an optional options object.

This object allows you to specify whether to enable high accuracy, a maximum age for the returned position value (up until this age it will be cached and reused if the same position is requested again; after this the browser will request fresh position data), and a timeout value that dictates how long the browser should attempt to get the position data for, before it times out.

A call towatchPosition could look like:

function success(position) {  doSomething(position.coords.latitude, position.coords.longitude);}function error() {  alert("Sorry, no position available.");}const options = {  enableHighAccuracy: true,  maximumAge: 30000,  timeout: 27000,};const watchID = navigator.geolocation.watchPosition(success, error, options);

Describing a position

The user's location is described using aGeolocationPosition object instance, which itself contains aGeolocationCoordinates object instance.

TheGeolocationPosition instance contains only two things, acoords property that contains theGeolocationCoordinates instance, and atimestamp property that contains a timestamp, given asUnix time in milliseconds, at which the position data was retrieved.

TheGeolocationCoordinates instance contains a number of properties, but the two you'll use most commonly arelatitude andlongitude, which are what you need to draw your position on a map. Hence many Geolocation success callbacks look fairly simple:

function success(position) {  const latitude = position.coords.latitude;  const longitude = position.coords.longitude;  // Do something with your latitude and longitude}

You can however get a number of other bits of information from aGeolocationCoordinates object, including altitude, speed, what direction the device is facing, and an accuracy measure of the altitude, longitude, and latitude data.

Handling errors

The error callback function, if provided when callinggetCurrentPosition() orwatchPosition(), expects aGeolocationPositionError object instance as its first parameter. This object type contains two properties, acode indicating what type of error has been returned, and a human-readablemessage that describes what the error code means.

You could use it like so:

function errorCallback(error) {  alert(`ERROR(${error.code}): ${error.message}`);}

Examples

In the following example the Geolocation API is used to retrieve the user's latitude and longitude. If successful, the available hyperlink is populated with anopenstreetmap.org URL that will show their location.

body {  padding: 20px;  background-color: #ffffc9;}button {  margin: 0.5rem 0;}

HTML

<button>Show my location</button><br /><p></p><a href="">Location unknown</a>

JavaScript

function geoFindMe() {  const status = document.querySelector("#status");  const mapLink = document.querySelector("#map-link");  mapLink.href = "";  mapLink.textContent = "";  function success(position) {    const latitude = position.coords.latitude;    const longitude = position.coords.longitude;    status.textContent = "";    mapLink.href = `https://www.openstreetmap.org/#map=18/${latitude}/${longitude}`;    mapLink.textContent = `Latitude: ${latitude} °, Longitude: ${longitude} °`;  }  function error() {    status.textContent = "Unable to retrieve your location";  }  if (!navigator.geolocation) {    status.textContent = "Geolocation is not supported by your browser";  } else {    status.textContent = "Locating…";    navigator.geolocation.getCurrentPosition(success, error);  }}document.querySelector("#find-me").addEventListener("click", geoFindMe);

Result