Client-side scripting: Difference between revisions

Revision as of 09:39, 6 September 2002

Revision as of 16:47, 20 July 2004

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'''Client-side scripting''' is a part of the [[DHTML]] (dynamic HTML) concept. It enables [[web-pages page]]s to be [[Script (computer programming)|scripted]]; that is, to have different and changing content depending on user [[input]], environmental conditions (such as the time of day), or other variables.

ClientWeb authors write client-side scriptingscripts isin donelanguages usingsuch scriptingas languages[[JavaScript]] foror web-browsers[[VBScript]], thesewhich are based on several standards.:

*[[HTML Scripting]]

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*[[Document Object Model]]

Client-side scripts are often embedded within an HTML document, but they may also be contained in a separate [[Computer file|file]], which is referenced by the document (or documents) that use it. Upon request, the necessary files are sent to the user's computer by the [[web server]] (or servers) on which they reside. The user's [[web browser]] [[Execution (computers)|executes]] the script, then displays the document, including any visible output from the script. Client-side scripts may also contain instructions for the browser to follow if the user interacts with the document in a certain way, e.g., clicks a certain button. These instructions can be followed without further communication with the server, though they may require such communication.

Client-side scripts is most commonly written using [[JavaScript]] or [[VBScript programming language|VBScript]].

By viewing the file that contains the script, users may be able to see its [[source code]]. Many web authors learn how to write client-side scripts partly by examining the source code for other authors' scripts.

In contrast, [[server-side scripting|server-side scripts]], written in languages such as [[Perl]] and [[PHP]], are executed by the web server when the user requests a document. They produce output in a format understandable by web browsers (usually [[HTML]]), which is then sent to the user's computer. The user cannot see the script's source code (unless the author publishes the code separately), and may not even be aware that a script was executed. The documents produced by server-side scripts may, of course, contain client-side scripts.

Client-side scripts have greater access to the information and functions available on the user's computer, whereas server-side scripts have greater access to the information and functions available on the server. Server-side scripts require that their language's [[Interpreter (computing)|interpreter]] is installed on the server, and produce the same output regardless of the client's browser, [[operating system]], or other system details. Client-side scripts do not require additional software on the server (making them popular with authors who lack administrative access to their servers); however, they do require that the user's web browser understands the scripting language in which they are written. It is therefore impractical for an author to write scripts in a language that is not supported by the web browsers used by a majority of his or her audience.

Unfortunately, even languages that are supported by a wide variety of browsers may not be implemented in precisely the same way across all browsers and operating systems. Authors are well-advised to review the behavior of their client-side scripts on a variety of [[Platform (computing)|platforms]] before they put them into use.