JavaScript engine
As JavaScript started being used more an more as a general-purpose language, execution speed, or how quickly the code is run, became more important for JavaScript engines. In response, many engines, such as V8 (Used in Chrome and Chromium) and SpiderMonkey (used in Firefox), started using Just-In-Time Compilation. In this method, it starts by compiling all of the code to optimized machine code, which is typically faster than interpretation, then running the result.