AJavaScript engine is a program that runsJavaScript code.Web Browsers often have a JavaScript engine. It can also be used outside of web browsers, such as running services inNode.js or apps in the electronframework.
JavaScript was originally created as ascripting language to allowweb pages to have changing, or dynamic, elements. Early Javascript engines were created asinterpreters, programs that simply read the script and execute the instructions without analyzing it any more.
As JavaScript started being used more and more as ageneral-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 inChrome andChromium) and SpiderMonkey (used inFirefox), started using Just-In-Time Compilation. In this method, it starts bycompiling all of the code to optimizedmachine code, which is typically faster than interpretation, then running the result.[1][2]
