JavaScript Engines in Major Web Browsers

JavaScript engines are programs that execute JavaScript code in web browsers and other environments. Each major browser has its own JavaScript engine, optimized for performance, security, and compatibility. These engines convert JavaScript code into machine code that computers can understand and execute efficiently.

Here’s a look at the JavaScript engines used in all major web browsers:

1. V8 (Google Chrome, Microsoft Edge, Opera, Node.js)

Browser: Google Chrome, Microsoft Edge, Opera
Developer: Google
First Released: 2008
Key Features:
Compiles JavaScript directly into machine code for faster execution.
Uses Just-In-Time (JIT) Compilation to improve performance dynamically.
Includes an Ignition interpreter and a TurboFan optimizing compiler to balance speed and memory efficiency.
Supports WebAssembly for running high-performance applications in the browser.
Powers Node.js, allowing JavaScript to run on servers.
2. SpiderMonkey (Mozilla Firefox)

Browser: Mozilla Firefox
Developer: Mozilla
First Released: 1996
Key Features:
The first-ever JavaScript engine, originally created by Brendan Eich in 10 days.
Uses a multi-tiered JIT compiler (Baseline, IonMonkey, and Warp) to optimize execution.
Supports Garbage Collection (GC) tuning to manage memory efficiently.
Implements Wasm (WebAssembly) for running compiled languages like C and Rust in the browser.
Constantly improved with better optimizations for modern JavaScript features.
3. JavaScriptCore (Safari – also called Nitro)

Browser: Apple Safari
Developer: Apple
First Released: 2003 (as JavaScriptCore), rebranded as Nitro in 2009
Key Features:
Uses a multi-tier JIT compiler with three stages: LLInt (interpreter), baseline JIT, and optimizing JIT.
Focuses on low memory usage and power efficiency, making it ideal for Apple devices.
Supports WebAssembly and modern ECMAScript features.
Features FTL (Fourth Tier LLVM JIT) optimization for improved performance.
Enhances security with sandboxing and memory protection.
4. Chakra (Legacy Microsoft Edge – Discontinued)

Browser: Microsoft Edge (before switching to Chromium)
Developer: Microsoft
First Released: 2009
Key Features:
Used in Internet Explorer 9-11 and the legacy Edge browser (before switching to V8 in 2020).
Had a multi-threaded JIT compiler that improved JavaScript execution.
Open-sourced as ChakraCore but is no longer actively developed.
Replaced by V8 when Microsoft Edge switched to Chromium.
5. Hermes (React Native)

Platform: React Native (for mobile apps)
Developer: Meta (formerly Facebook)
First Released: 2019
Key Features:
Designed for mobile performance in React Native applications.
Uses Ahead-Of-Time (AOT) compilation, reducing app startup time.
Optimized for low memory usage, making it ideal for mobile devices.
Supports ECMAScript features commonly used in React applications.
Comparison Table of JavaScript Engines

JavaScript Engine Browsers/Platforms Compilation Type Special Features
V8 Chrome, Edge, Opera, Node.js JIT TurboFan, WebAssembly, Fast execution
SpiderMonkey Firefox JIT Multi-tier compiler, WebAssembly support
JavaScriptCore (Nitro) Safari JIT Low power usage, FTL optimization
Chakra (Discontinued) Legacy Edge, IE 9-11 JIT Multi-threaded JIT, ChakraCore (open-source)
Hermes React Native AOT Optimized for mobile, fast startup
Conclusion

JavaScript engines are the backbone of modern web browsers, enabling fast and efficient execution of JavaScript code. While V8 dominates the market due to Chrome and Node.js, SpiderMonkey and JavaScriptCore remain crucial for Firefox and Safari, respectively. Although Chakra has been discontinued, Hermes is emerging as an important engine for mobile development.

Each engine continues to evolve, ensuring better performance, security, and support for the latest JavaScript standards.