For a web page to be viewed, its associated HTML document is accessed from the server, the layout instructions contained in the document are interpreted by the browser, and the results are displayed. It is important to remember that HTML is a markup language, not a programming language . Even when users enter data on the page, say through the use of forms, that data cannot be manipulated arithmetically or logically by the HTML language. This is because the language does not contain the processing commands common to programming languages. For many Web applications this lack of processing commands is no great drawback.
Most web pages are simple displays of information for which no processing is required.
Still, there are cases where availability of processing commands to the web page can be a great asset. A first step towards making web pages more interactive with users and more responsive to their information processing needs is the use of scripting languages . A scripting language permits web authors to write processing routines, called scripts , and to integrate them within the HTML layout code. These scripts, which act like program subroutines, can perform many of the data manipulation and logical functions of full-featured programming languages. In fact, a scripting language is often a subset of a full-featured language.