Narcissus is an open source

Open source

The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 JavaScript engine

JavaScript engine

A JavaScript engine is specialized computer software which interprets and executes JavaScript . Although there are several uses for a JavaScript engine, it is most commonly used in web browsers.-History:...

. It was written by Brendan Eich

Brendan Eich

Brendan Eich is a computer programmer and creator of the JavaScript scripting language. He is the chief technology officer at the Mozilla Corporation.-Education:...

, who also wrote the first JavaScript engine, SpiderMonkey. Its name is based on the mythical figure of Narcissus

Narcissus (mythology)

Narcissus or Narkissos , possibly derived from ναρκη meaning "sleep, numbness," in Greek mythology was a hunter from the territory of Thespiae in Boeotia who was renowned for his beauty. He was exceptionally proud, in that he disdained those who loved him...

, who fell in love with himself. This relates to the fact that this JavaScript engine is a metacircular interpreter, because the engine itself is also written in JavaScript

JavaScript

JavaScript is a prototype-based scripting language that is dynamic, weakly typed and has first-class functions. It is a multi-paradigm language, supporting object-oriented, imperative, and functional programming styles....

, albeit using non-standard extensions that are specific to SpiderMonkey.

The Narcissus engine can be plugged into Firefox via Zaphod add-on to run scripts on web pages. Since Narcissus has a simpler code-base than "real" JavaScript engines, it can be used to prototype new language features with less effort.