In computer programming, a script is a program or sequence of instructions that is translated and executed by another program (e.g., a Web browser) rather than by a compiler or interpreter.

Some languages have been conceived expressly as scripting languages. Among the most popular are Perl, VBScript, JavaScript, and Tcl/Tk. In the context of the World Wide Web, Perl, VBScript, and similar scripting languages are often written to handle forms input or other services for a Web site and are processed on the Web server. A JavaScript script in a Web page runs "client-side" as it is translated and executed by the Web browser.

Client-side scripting is based on the recognition that the computer which the client is using to browse the Web has quite a bit of computing power that is not being utilized. At the same time, the Web servers are handling hundreds of CGI requests in addition to their regular duties. Thus, it makes sense to share some of that computing burden between the client and server by taking some of the processing load off the server and giving it to the client.

Typically, much of what a CGI program does can be accomplished on the client's computer. The only time the server needs to be involved is when the Web application needs to send email or access datafiles. Things like maintaining state, filling out forms, error checking, or performing numeric calculations, can be easily handled by the client's computer. The Web browser need not check back with a CGI program each time the user does something. A "script-enabled" HTML page can carry with it instructions on how to handle a number of common events.

In general, scripting languages are easier and faster to code in than the more structured and compiled languages such as C and C++ and are ideal for programs of very limited capability or that can reuse and tie together existing compiled programs. However, a script takes longer to run than a compiled program since each instruction is being handled by another program first (requiring additional instructions) rather than directly by the basic instruction processor.

Dynamic HTML (DHTML) is a collective term for a combination of new Hypertext Markup Language (HTML) tags and options, style sheets, and programming that will let you create Web pages more animated and more responsive to user interaction than previous versions of HTML.

Much of DHTML is specified in HTML 4.0. Simple examples of dynamic HTML pages would include (1) having the color of a text heading change when a user passes a mouse over it (try it with the heading above), or (2) allowing a user to "drag and drop" an image to another place on a Web page. Dynamic HTML can allow Web documents to look and act like desktop applications or multimedia productions.

This three-credit course covers an introduction to the Document Object model (DOM), JavaScript and VBScript scripting languages, Java Applets, cascading style sheets, browser recognition, browser-specific content, data validation, and layers.

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