Coding with JavaScript For Dummies
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JavaScript code writers need to have a form grasp on geolocation. The Geolocation API gives programs access to the web browser’s geolocation functionality, which can tell the program the device’s location on Earth. The Geolocation API is among the most well-supported HTML5 APIs and is implemented in about 90 percent of desktop and mobile browsers, including all of the big ones, except for Opera Mini.

What does geolocation do?

The Geolocation API describes how JavaScript can interact with the

navigator.geolocation object in order to get data about a device’s current position, including

  • Latitude: The latitude in decimal degrees

  • Longitude: The longitude in decimal degrees

  • Altitude: The altitude in meters

  • Heading: The direction the device is traveling

  • Speed: The velocity of the device in meters per second

  • Accuracy: The accuracy of the latitude and longitude, measured in meters

By obtaining some or all of this data, a JavaScript application running in a web browser can place a user on a map, query sources such as Google Maps for landmarks or restaurants local to the user, and much more.

How does geolocation work?

When JavaScript initiates a request for the devices position, through the Geolocation object, a number of steps take place, prior to the position information being returned.

The first thing to happen is that the browser needs to make sure that the user has given permission for the particular web app to access the device’s geolocation information. Different browsers prompt the user for permission in different ways, but it’s typically done through some sort of popup or notification.

The Chrome browser displays a geolocation icon and a message below the address bar when a website requests access to geolocation data.

Chrome displays geolocation requests below the address bar.
Chrome displays geolocation requests below the address bar.

After you give a website access to your geolocation data, the browser tries to find you. It does this through a number of different means, starting with the most accurate and proceeding through to less accurate ways.

If the program indicates that high accuracy is required, geolocation will spend a longer time trying to access highly accurate GPS information. Otherwise, the browser will attempt to balance speed with accuracy to obtain the most accurate results from any of the following sources, when available:

  • GPS satellite positioning

  • Your wireless network connection

  • The cell tower your phone or mobile device is connected to

  • The IP address of your device or computer

How do you use geolocation?

The key to using geolocation is the navigator.geolocation object’s getCurrentPosition method. The getCurrentPosition method can take three arguments:

  • success: A callback function that’s passed a Position object when geolocation is successful

  • error: An optional callback function that’s passed the PositionError object when geolocation fails

  • options: An optional PositionOptions object that can be used to control several aspects of how the geolocation lookup is performed

The Position object that’s returned by the getCurrentPosition method contains two properties:

  • Position.coords: Contains a Coordinates object that describes the location

  • Position.timestamp: The time when the location was retrieved

This example shows how you can use the getCurrentPosition method to get the Position object and loop through the return values in Position.coords.

 <title>The Position object</title>
 var gps = navigator.geolocation.getCurrentPosition(
 function (position) {
  for (key in position.coords) {
  document.write(key+’: ‘+ position.coords[key]);
  document.write (‘<br>‘);

If the device you run this code on supports geolocation and the browser can determine your location, the results of running this script should resemble this.

Printing the return values of the<span class=
Position obje" width="535"/>
Printing the return values of the Position object.

Notice that several of the properties of the Coordinates object are all null. This is because it was run using a desktop computer that doesn’t have the ability to get some of these coordinates. The result of running the same script in a mobile browser on a smartphone:

Getting geolocation data with a smartphone browser.
Getting geolocation data with a smartphone browser.

Notice that the mobile browser displays figures for altitude, but heading and speed are still null because the device was stationary at the time when the page was loaded.

About This Article

This article is from the book:

About the book authors:

Chris Minnick is an accomplished author, trainer, and web developer who has worked on web and mobile projects for both small and major businesses. Eva Holland is an experienced writer and trainer who has designed and taught online, in-person, and video courses. They are cofounders of WatzThis?

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