explaingit

ahaoboy/es5

Analysis updated 2026-05-18

★ 2RustAudience · developerComplexity · 2/5LicenseSetup · easy

TLDR

A small, MuJS-compatible JavaScript engine written in Rust, usable as a command line interpreter, script runner, or REPL.

Mindmap

mindmap
  root((es5))
    What it does
      JavaScript engine
      MuJS-compatible
      ES5 focused
    Tech stack
      Rust
      MuJS
    Use cases
      Run JS scripts
      Interactive REPL
      Benchmark comparisons
      Power es5-react
    Audience
      Developers

Code map

Detail Auto

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filefunction / class

What do people build with it?

USE CASE 1

Evaluate or run JavaScript files from the command line using a lightweight Rust-based engine.

USE CASE 2

Compare this engine's speed against other small JavaScript engines using its public benchmark page.

USE CASE 3

Embed the engine as the JavaScript runtime behind another tool, as es5-react does for terminal React rendering.

USE CASE 4

Open an interactive REPL to try out small pieces of ES5 JavaScript.

What is it built with?

RustJavaScriptMuJS

How does it compare?

ahaoboy/es5132ikl/game1lystore/pay-dcp
Stars222
LanguageRustRustRust
Last pushed—2020-12-30—
Maintenance—Dormant—
Setup difficultyeasymoderatemoderate
Complexity2/52/53/5
Audiencedevelopergeneraldeveloper

Figures from each repo's GitHub metadata at analysis time.

How do you get it running?

Difficulty · easy Time to first run · 5min
MIT license: free to use, modify, and distribute for any purpose, including commercial use, as long as you keep the copyright notice.

In plain English

es5 is a small JavaScript engine written in the Rust programming language. It aims to be compatible with MuJS, an existing lightweight JavaScript interpreter written in C, and it is based on a specific version of that project, adjusted to follow the older ES5 version of the JavaScript language more strictly. The README is fairly short and mostly covers how to install and run it. You can build it with Cargo, Rust's package manager, then use the resulting command line tool in a few ways: evaluate a single line of JavaScript directly, run a JavaScript file, pipe code into it through standard input, or open an interactive prompt where you can type JavaScript and see results immediately. The project also tracks its own speed against other small JavaScript engines, including Boa, MuJS itself, and a project called Lumen, with a public benchmark page linked from the README so anyone can compare results. A separate, related project called es5-react uses this engine to render React components directly in a terminal window instead of a browser, using es5 as the JavaScript runtime that powers it. The README does not go into detail about which parts of the JavaScript language are supported or how complete the implementation is beyond aiming for ES5 compatibility, so anyone considering it for real use would need to check the source or try it directly. It is released under the MIT license.

Copy-paste prompts

Prompt 1
Help me install es5 with cargo binstall and run a simple JavaScript expression with it.
Prompt 2
Show me how to use es5 as an interactive REPL for testing JavaScript snippets.
Prompt 3
Explain how es5 compares in speed to Boa, MuJS, and Lumen based on its benchmark page.
Prompt 4
Help me understand how es5-react uses this engine to render React components in a terminal.

Frequently asked questions

What is es5?

A small, MuJS-compatible JavaScript engine written in Rust, usable as a command line interpreter, script runner, or REPL.

What language is es5 written in?

Mainly Rust. The stack also includes Rust, JavaScript, MuJS.

What license does es5 use?

MIT license: free to use, modify, and distribute for any purpose, including commercial use, as long as you keep the copyright notice.

How hard is es5 to set up?

Setup difficulty is rated easy, with roughly 5min to a first successful run.

Who is es5 for?

Mainly developer.

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