JavaScript: The Definitive Guide, Fourth Edition

Client-Side JavaScript Features

Another possible use of JavaScript is for writing programs to perform arbitrary computations. You can write simple scripts, for example, that compute Fibonacci numbers, or search for primes. In the context of the Web and web browsers, however, a more interesting application of the language might be a program that computed the sales tax on an online order, based on information supplied by the user in an HTML form. As mentioned earlier, the real power of JavaScript lies in the browser and document-based objects that the language supports. To give you an idea of JavaScript’s potential, the following sections list and explain the important capabilities of client-side JavaScript and the objects it supports.

Control Document Appearance and Content

The JavaScript Document object, through its write( ) method, which we have already seen, allows you to write arbitrary HTML into a document as the document is being parsed by the browser. For example, you can include the current date and time in a document or display different content on different platforms.

You can also use the Document object to generate documents entirely from scratch. Properties of the Document object allow you to specify colors for the document background, the text, and the hypertext links within it. This amounts to the ability to generate dynamic and conditional HTML documents, a technique that works particularly well in multiframe documents. Indeed, in some cases dynamic generation ...