JavaScript® Bible, Sixth Edition

Chapter 39. The Navigator and Other Environment Objects

IN THIS CHAPTER

• Determining which browser the user has

• Branching scripts according to the user's operating system

• Detecting plug-in support

Client-side scripting primarily focuses on the document inside a browser window and the content of the document. As discussed in Chapter 16, the window, too, is an important part of how you apply JavaScript on the client. But stepping out even one more level is the browser application itself. Scripts sometimes need to know about the browser and the computing environment in which it runs so that they can tailor dynamic content for the current browser and operating system.

To that end, browsers provide objects that expose as much about the client computer and the browser as is feasible within accepted principles of preserving a user's privacy. In addition to providing some of the same information that server-side programs receive as environment variables, these browser-level objects in some browsers also include information about how well equipped the browser is with regard to plug-ins and Java. Another object reveals information about the user's video monitor, which may influence the way your scripts calculate information displayed on the page.

The objects in this chapter don't show up on the document object hierarchy diagrams, except as free-standing groups (see Appendix A). The IE4+ object model, however, incorporates these environmental objects as properties of the window object. Because the ...