Cross Platform Component Object Model (XPCOM) is a

cross-platform In computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several computing platforms. Some cross-platform software ...

component model Component-based software engineering (CBSE), also called component-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a give ...

from

Mozilla Mozilla (stylized as moz://a) is a free software community founded in 1998 by members of Netscape. The Mozilla community uses, develops, spreads and supports Mozilla products, thereby promoting exclusively free software and open standards, ...

. It is similar to Microsoft Component Object Model (COM) and Common Object Request Broker Architecture (CORBA). It features multiple language bindings and interface description language (IDL) descriptions; thus programmers can plug their custom functions into the framework and connect it with other components. The most prominent usage of XPCOM is within the Firefox web browser. Many of its internal components interact via XPCOM interfaces. Furthermore, Firefox used to allow add-ons extensive XPCOM access, but this was removed in 2017 and replaced with the less-permissive WebExtensions API. (Three

forks In cutlery or kitchenware, a fork (from la, furca 'pitchfork') is a utensil, now usually made of metal, whose long handle terminates in a head that branches into several narrow and often slightly curved tines with which one can spear foods eit ...

of Firefox still support the legacy add-on capability: Pale Moon,

Basilisk In European bestiaries and legends, a basilisk ( or ) is a legendary reptile reputed to be a serpent king, who causes death to those who look into its eyes. According to the '' Naturalis Historia'' of Pliny the Elder, the basilisk of Cyre ...

, Waterfox.)

Model

XPCOM is one of the main things making the

application environment an actual framework. It is a development environment that provides the following features for the cross-platform software developer: * Component management * File abstraction * Object message passing * Memory management This component object model makes virtually all of the functionality of

Gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos a ...

available as a series of components, or reusable cross-platform libraries, that can be accessed from the

web browser A web browser is application software for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used o ...

or scripted from any Mozilla application. Applications that must access the various Mozilla XPCOM libraries (

networking Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematic ...

security" \n\n\nsecurity.txt is a proposed standard for websites' security information that is meant to allow security researchers to easily report security vulnerabilities. The standard prescribes a text file called \"security.txt\" in the well known locat ...

, DOM, etc.) use a special layer of XPCOM called XPConnect, which reflects the library interfaces into

JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...

, or other languages. XPConnect glues the front end to the C++, C, or

Rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...

programming language based components in XPCOM, and it can be extended to include scripting support for other languages: PyXPCOM already offers support for Python. PerlConnect and plXPCOM provide support for

Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...

, and there are efforts underway to add

Common Language Infrastructure The Common Language Infrastructure (CLI) is an open specification and technical standard originally developed by Microsoft and standardized by ISO/IEC (ISO/IEC 23271) and Ecma International (ECMA 335) that describes executable code and a ...

(CLI) and

Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called ...

language support for XPConnect. For developers, XPCOM allows writing components in C++, C,

, Python, or other languages for which special bindings have been created, and compile and run those components on dozens of different platforms, including these and others where Mozilla is supported. The flexibility to reuse the XPCOM components from the Gecko library and develop new components that run on different platforms facilitates

rapid application development Rapid application development (RAD), also called rapid application building (RAB), is both a general term for adaptive software development approaches, and the name for James Martin's method of rapid development. In general, RAD approaches to ...

and results in an application that is more productive and easier to maintain. The networking library, for example, is a set of XPCOM components that can be accessed and used by any Mozilla application. File I/O, security, password management, and profiles are also separate XPCOM components that programmers can use in their own application development.

Past overuse

XPCOM adds a lot of code for marshalling objects, and in the Netscape era XPCOM was overused for internal interfaces where it wasn't truly necessary, resulting in

software bloat Software bloat is a process whereby successive versions of a computer program become perceptibly slower, use more memory, disk space or processing power, or have higher hardware requirements than the previous version, while making only dubious us ...

. This was a key reason why in 2001

Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...

forked KHTML, not Gecko, to create the

WebKit WebKit is a browser engine developed by Apple and primarily used in its Safari web browser, as well as on the iOS and iPadOS version of any web browser. WebKit is also used by the BlackBerry Browser, PlayStation consoles beginning from the ...

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...

for its Safari browser. Mozilla has since cleaned up some of the XPCOM bloat. By 2008, this combined with other efforts resulted in big performance improvements for

References

External links

XPCOM API ReferenceXPCOM Project Homepage
* ttp://www.codeproject.com/Articles/87465/A-Simple-XPCOM-Tutorial A Simple XPCOM Tutorial {{DEFAULTSORT:Xpcom Application programming interfaces Mozilla