Training Guide: Programming in HTML5 with JavaScript and CSS3 Ebook

540 CHAPTER 14 Making your HTML location-aware

Before you begin

To complete this book, you must have some understanding of web development. This chapter

requires the hardware and software listed in the “System requirements” section in the book’s

Introduction.

Lesson 1: Basic positioning

The Geolocation object is accessible by using the navigator.geolocation global variable. Most

browsers support the Geolocation API, and the following code can be used to determine

whether the user’s browser provides support.

function supportsGeolocation() {

return 'geolocation' in navigator;

}

This code checks whether a geolocation property is on the object that’s referenced by the

navigator global variable. If the property exists, it will reference a Geolocation object.

After this lesson, you will be able to:

■■Understand the Geolocation object.

■■Retrieve the current position.

■■Handle positioning errors.

Estimated lesson time: 20 minutes

Geolocation object reference

The Geolocation object has a simple API with the following methods.

■■getCurrentPosition() Method that accepts a success callback, an error callback, and

options array and calls the success callback with the current position

■■watchPosition() Method that accepts a success callback, an error callback, and

options array and continuously calls the success callback with the current position

■■clearWatch() Method that stops continuous calling that was started by using the

watchPosition method

Notice that the getCurrentPosition and watchPosition methods have the same parameters.

The Position object has the following properties.

■■coords Gets a Coordinates object that contains information about the current

position.