In [[distributed computing]], '''code on demand''' is a general term for any technology that sends executable software code from a server computer to a client computer upon request from the client's software.
Code on demand is a specific use of [[mobile code]], within the field of [[Codecode mobility]].<ref name="Understanding Code Mobility">{{cite journal|last=Fuggetta|first=Alfonso|author2=Gian Pietro Picco |author3=Giovanni Vigna |year=1998|title=Understanding Code Mobility|journal=IEEE Transactions on Software Engineering|publisher=IEEE Press Piscataway|___location=NJ, USA|volume=24|issue=5|pages=342–361|issn=0098-5589|url=http://www2.computer.org/portal/web/csdl/abs/trans/ts/1998/05/e0342abs.htm|accessdate=29 July 2009|doi=10.1109/32.685258}}</ref>
== Examples ==
Some well-known examples forof the code on demand paradigm on the web are [[Java applet]]s, Adobe’s [[ActionScript]] language for the [[Flashplayer|Flash player]], and [[JavaScript]]:<ref name="Is Code Still Moving Around">{{cite journal|last= Carzaniga|first=Antonio|author2=Gian Pietro Picco |author3=Giovanni Vigna |year=2007|title=Is Code Still Moving Around? Looking Back at a Decade of Code Mobility|journal=ICSE COMPANION '07 Companion to the proceedings of the 29th International Conference on Software Engineering|publisher=IEEE Computer Society|___location=Washington, DC, USA|pages=9–20|url=http://dl.acm.org/citation.cfm?id=1248922|doi=10.1109/ICSECOMPANION.2007.44}}</ref> The program code lies inactive on a [[web server]] until a user (client) requests a web page that contains a link to the code using the client's [[web browser]]. Upon this request, the web page and the program are transported to the user's machine using [[HTTP]]. When the page is displayed, the code is started in the browser and executes locally, inside the user's computer until it is stopped (e.g., by the user leaving the web page).
