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'''Welcome to JavaScript Essentials'''

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 dictated that an entirely new web page be loaded in order to display new information.

It quickly became clear that a way of performing "client-side" or "web browser-side" processing was needed. The original intent for JavaScript, therefore, was to address this need by facilitating such tasks as validating user input before it is transmitted to the web server, and creating dynamic web page content and layouts independently of the web server (for example, displaying different text depending on a user's actions within the page). 

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, JavaScript 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.

The purpose of this book, therefore, is to provide the essentials of JavaScript so that anyone with a web site can use this powerful scripting language quickly and effectively without having to learn things that, whilst within the capabilities of JavaScript, aren't actually needed by the average web designer. That said this book does not take any shortcuts. It provides detailed and in depth knowledge of all aspects of JavaScript from language basics through to advanced topics.

This book is designed to provide a detailed and comprehensive, yet easy to follow, guide to developing powerful, dynamic web pages using JavaScript. It could be said that the object of '''JavaScript Essentials''' is to provide you with everything you need to use JavaScript, and nothing that you don't.