JavaScript engines are responsible for parsing, compiling, and executing JavaScript code. ### V8 (Google) - Used in Chrome, Edge, Node.js, Deno. - Highly optimized with JIT (Just-In-Time) compilation. - Converts JavaScript to native machine code using: - Ignition (interpreter) - TurboFan (optimizer) ### SpiderMonkey (Mozilla) - Used in Firefox. - First-ever JavaScript engine. - Uses JIT compilation with: - Baseline - IonMonkey ### JavaScriptCore (Nitro) (Apple) - Used in Safari, React Native. - Developed by Apple. - Uses LLVM-based JIT compilation. ### Chakra (Microsoft) - Used in older versions of Edge. - Microsoft has since switched Edge to V8. ### Hermes (Meta/Facebook) - Used in React Native. - Optimized for mobile devices with ahead-of-time compilation. > Each runtime chooses an engine based on its needs, with V8 being the most widely used across browsers and server-side environments.