JavaScript: The Definitive Guide, 6th Edition

Chapter 13. JavaScript in Web Browsers

The first part of this book described the core JavaScript language. We now move on to JavaScript as used within web browsers, commonly called client-side JavaScript. Most of the examples we’ve seen so far, while legal JavaScript code, have no particular context; they are JavaScript fragments that run in no specified environment. This chapter provides that context.

Before we begin talking about JavaScript, it is worth thinking about the web pages we display in web browsers. Some pages present static information and can be called documents. (The presentation of that static information may be fairly dynamic—because of JavaScript—but the information itself is static.) Other web pages feel more like applications than documents. These pages might dynamically load new information as needed, they might be graphical rather than textual, and they might operate offline and save data locally so they can restore your state when you visit them again. Still other web pages sit somewhere in the middle of the spectrum and combine features of both documents and applications.

This chapter begins with an overview of client-side JavaScript. It includes a simple example and a discussion of the role of JavaScript in both web documents and web applications. That first introductory section also explains what is coming in the Part II chapters that follow. The sections that follow explain some important details about how JavaScript code is embedded and executed within ...