How do I compile JavaScript to bytecode with MQuickJS?

Use the mqjs tool with the -o option, e.g., './mqjs -o output.bin script.js', to generate bytecode that can be saved to ROM and executed later with the -b flag, as shown in the REPL section.

MQuickJS vs QuickJS: which one should I use?

MQuickJS is optimized for embedded systems with ultra-low memory (10 kB RAM), while QuickJS offers full JavaScript support for general use. Choose MQuickJS only if memory is critically constrained; otherwise, QuickJS provides more features and ease.

Can MQuickJS run ES6 arrow functions or async/await?

No, MQuickJS only supports a subset of ES5, so modern ES6+ features like arrow functions, classes, and async/await are not available, as outlined in the JavaScript Subset Reference.

How to integrate MQuickJS into a C project?

Include mquickjs.h, provide a memory buffer with JS_NewContext, and use the C API with careful GC reference handling, as demonstrated in example.c and the C API section.

What is the memory footprint for a simple 'Hello World' in MQuickJS?

MQuickJS can run with as little as 10 kB of RAM, but actual usage depends on the script. Use the --memory-limit option in mqjs to test and constrain memory consumption for specific applications.

Is MQuickJS suitable for real-time systems?

It may be, due to deterministic memory allocation and no malloc dependency, but the tracing GC could introduce pauses; performance testing is recommended, as benchmarks like Octane are provided but not tailored for real-time.

Open-Awesome

MicroQuickJS

NOASSERTIONC

A JavaScript engine for embedded systems requiring as little as 10 kB of RAM, implementing a stricter ES5 subset.

GitHub

5.7k stars216 forks0 contributors

What is MicroQuickJS?

MicroQuickJS is a JavaScript engine designed for embedded systems and resource-constrained devices. It compiles and runs JavaScript programs using extremely low memory—as little as 10 kB of RAM—while implementing a stricter, safer subset of ES5 JavaScript. It solves the problem of running JavaScript in environments where traditional engines like V8 or SpiderMonkey are too resource-intensive.

Target Audience

Embedded systems developers, IoT engineers, and anyone working on microcontrollers or low-memory devices who need to run JavaScript code efficiently and safely.

Value Proposition

Developers choose MQuickJS for its ultra-low memory footprint, deterministic memory usage without relying on system malloc, and its stricter JavaScript subset that prevents common errors, making it ideal for reliable embedded applications.

Overview

Public repository of the Micro QuickJS Javascript Engine

Use Cases

Best For

Running JavaScript on microcontrollers with limited RAM
Embedded systems requiring deterministic memory allocation
IoT devices where a full JavaScript engine is too heavy
Educational projects exploring minimal JS engines
Applications needing JavaScript bytecode execution from ROM
Environments where a stricter, safer JS subset is preferred

Not Ideal For

Web applications requiring full ES2020+ support and npm ecosystem integration
Projects that rely on direct eval for dynamic code execution or metaprogramming
Environments where memory is abundant and maximum JavaScript performance is the top priority
Development teams looking for a plug-and-play JavaScript engine with extensive documentation and community support

Pros & Cons

Pros

Ultra-Low Memory Footprint

Runs with as little as 10 kB of RAM and 100 kB of ROM, demonstrated by the --memory-limit option in the REPL, making it ideal for embedded systems.

Stricter JavaScript Safety

Enforces a subset of ES5 that forbids error-prone constructs like array holes and direct eval, reducing bugs in resource-constrained code.

Efficient Garbage Collection

Uses a tracing compacting GC to minimize fragmentation and allow smaller object representations, as detailed in the Internals section.

Minimal C Dependencies

Does not require standard malloc or printf, using a provided memory buffer instead, enhancing portability to bare-metal systems.

Cons

Limited JavaScript Features

Only supports a strict ES5 subset with missing modern features like full ES6, advanced regexp, and Date functions beyond Date.now().

Complex Memory Management

The C API requires careful handling with JS_PushGCRef and JS_PopGCRef, and objects can move during allocation, increasing development complexity.

No Bytecode Backwards Compatibility

Bytecode format is not guaranteed to be compatible across versions, as admitted in the README, requiring recompilation for updates.

Sparse Tooling and Ecosystem

Lacks the extensive libraries, debuggers, and community support of mainstream JavaScript engines, making development and troubleshooting harder.

Frequently Asked Questions

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