Before JavaScript was created a typical web browsing experience consisted largely of displaying static pages of information. Any type of user interaction with a web page usually involved the browser sending information back to the web server where some type of server based script or other program would validate the user's data input. The server would then send back either a static error page if the user had entered invalid data or, assuming successful validation, return a static page to the web browser containing the results of the transaction. In addition, the lack of a mechanism to implement dynamic web page content and behavior dictacted that an entirely new web page be loaded in order to display new information.
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It quickly became clear that a way of perfoming "client-side" or "web browser-side" processing was needed. The original intent for JavaScript, therefore, was to address this need by allowing such tasks as validating user input before it is transimitted to the web server, and creating dynamic web page content and layouts indendent of the web server (for example displaying different text depending on a user's actions within the page).
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JavaScript met and, indeed, exceeded these requirements by providing an extremely flexible and intuitive scripting language. The problem today is that, as with any useful technology, it has been used in ways never anticipated by its original authors. As a result, the potential uses of JavaScript have grown far beyond the needs of the average person looking to add dynamic behavior to web pages. The result of this is that JavaScript book authors also feel the need to cover every possible capability of JavaScript, often to the extent that the average JavaScript reference book now runs to over 1,000 pages.
