Bun is a JavaScript runtime, bundler, transpiler, npm package manager, and test runner all-in-one. It isn't accurate to say Bun is a JavaScript engine. We use

Bun is a JavaScript runtime, bundler, transpiler, npm package manager, and test runner all-in-one. It isn't accurate to say Bun is a JavaScript engine. We use JavaScriptCore as the engine, which is the same engine used by Safari (WebKit). The engine is responsible for running the code and a number of language APIs (Array, Object, Number, RegExp, etc). The runtime is responsible for things like I/O, filesystem access, the event loop, and implementing a very large number of non-language APIs and modules