What is JavaScript written in?
The major JavaScript engines are written in C++. Google's V8 (used in Chrome and Node.js), Mozilla's SpiderMonkey, and Apple's JavaScriptCore are all implemented in C++. The JavaScript language specification is defined by ECMAScript and doesn't mandate any particular implementation language.
Quick Facts
- Short answer
- Modern JavaScript engines are mostly C++
- Specification
- ECMAScript
- Major engines
- V8, SpiderMonkey, JavaScriptCore
- Historical note
- Original SpiderMonkey began in C
Details
JavaScript itself is a language standard, defined by ECMAScript. The useful implementation question is about JavaScript engines: the programs that parse, compile, optimize, and execute JavaScript code.
While the very first JavaScript engine was written in C, most modern major engines use C++ for performance-critical compiler and runtime code. V8 powers Chrome and Node.js, SpiderMonkey powers Firefox, and JavaScriptCore powers Safari and WebKit-based environments.
Major JavaScript engines
| Engine | Written in | Where it runs |
|---|---|---|
| V8 | C++ | Chrome, Node.js, Deno, Electron |
| SpiderMonkey | C++, Rust, JavaScript | Firefox |
| JavaScriptCore | C++ | Safari and WebKit |
The dataset keeps the historical C relationship for the original SpiderMonkey implementation, while the modern engine pages document C++-based implementations such as V8 and JavaScriptCore.
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