MicroQuickJS
A JavaScript engine for embedded systems requiring as little as 10 kB of RAM, implementing a stricter ES5 subset.
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.
Embedded systems developers, IoT engineers, and anyone working on microcontrollers or low-memory devices who need to run JavaScript code efficiently and safely.
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
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.
Enforces a subset of ES5 that forbids error-prone constructs like array holes and direct eval, reducing bugs in resource-constrained code.
Uses a tracing compacting GC to minimize fragmentation and allow smaller object representations, as detailed in the Internals section.
Does not require standard malloc or printf, using a provided memory buffer instead, enhancing portability to bare-metal systems.
Cons
Only supports a strict ES5 subset with missing modern features like full ES6, advanced regexp, and Date functions beyond Date.now().
The C API requires careful handling with JS_PushGCRef and JS_PopGCRef, and objects can move during allocation, increasing development complexity.
Bytecode format is not guaranteed to be compatible across versions, as admitted in the README, requiring recompilation for updates.
Lacks the extensive libraries, debuggers, and community support of mainstream JavaScript engines, making development and troubleshooting harder.
Frequently Asked Questions
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