JavaScript Engines of Major Browsers

# Introduction JavaScript engines are the core components that power our web browsing experience, serving as the invisible workhorses behind every modern browser. These sophisticated pieces of software parse, compile, and execute JavaScript code, transforming human-readable scripts into optimized machine instructions. As web applications have grown increasingly complex, browser vendors have engaged in fierce competition to create the fastest, most efficient engines. This article explores the major JavaScript engines powering today's popular browsers, examining their architectures, unique features, and the impact they have on web performance. ### JavaScript Engines of Major Browsers 1. #### V8 (Chrome, Edge, Opera) * Developed by Google for Chrome * Written in C++ * Uses Just-In-Time (JIT) compilation to convert JavaScript to machine code * Features like hidden classes and inline caching for optimized object property access * Garbage collection for memory management * Powers Node.js and Deno runtimes 2. #### SpiderMonkey (Firefox) * First JavaScript engine, originally created by Brendan Eich * Uses multi-tier JIT compilation approach * Features IonMonkey and Baseline compilers for optimization * Type inference system to improve performance * Implements ECMAScript standards with strong compliance 3. #### JavaScriptCore/Nitro (Safari) * Developed by Apple for WebKit * Multi-tier compilation architecture * Features like DFG (Data Flow Graph) JIT and FTL (Faster Than Light) JIT * B3 (Bare Bones Backend) low-level optimizer * Strong focus on energy efficiency for mobile devices 4. #### Hermes (React Native) * Facebook's JavaScript engine for React Native * Optimized for mobile apps * Focuses on startup time, package size, and memory usage * Precompiles JavaScript to bytecode 5. #### Chakra (Internet Explorer, legacy Edge) * Previously used in Internet Explorer and original Edge * JIT compilation with tiered optimization * Separate background garbage collection * Legacy engine as Edge now uses ### Conclusion JavaScript engines form the heart of modern web browsers, each with unique approaches to executing code. While they all comply with ECMAScript standards, their architectural differences significantly impact performance across platforms. V8 leads in pure speed and powers multiple environments beyond Chrome, while JavaScriptCore prioritizes energy efficiency crucial for mobile devices. SpiderMonkey maintains the original JavaScript legacy with robust standards compliance, and newer engines like Hermes target specialized use cases. As web applications grow more complex, these engines continuously evolve—improving parsing speed, memory management, and optimization techniques. Understanding these differences helps developers create more efficient cross-browser code and explains why performance can vary across browsers even with identical JavaScript. The ongoing competition between browser vendors ultimately benefits users through faster, more responsive web experiences.