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World's smallest JavaScript engine (8.5kB) for a restricted subset of the JavaScript language (see limitations below).

Microvium is an ultra-compact, embeddable scripting engine for microcontrollers for executing a useful subset of the JavaScript language, with a focus on small size and ease of use.

Microvium takes the unique approach partially running the JS code at build time and deploying a snapshot, which leads to a number of advantages over other embedded JavaScript engines. See

Take a look at my blog if you're interested in some of the behind-the-scenes thought processes and design decisions, and to stay updated with new developments. Or for more granular updates, follow me on Twitter at @microvium.

See also where an installer can be downloaded (for Windows only, at this time, and this is a bit out of date -- but contact me if you want the updated version).

Install and Get Started

Check out the Getting Started tutorial which explains the concepts, gives some examples, and shows how to get set up.


See also the set of supported language features.

  • Run high-level scripts on an MCU (bare metal or RTOS)
  • Run the same script code on small microcontrollers and desktop-class machines (ideal for IoT applications with shared logic between device and server) -- the engine is available as a C unit and as a node.js library.
  • Runs JavaScript on very small devices, requiring 8-16 kB of ROM depending on the platform and enabled features (for more details, see here).
  • Script code is completely sand-boxed and isolated for security and safety
  • Snapshotting: hibernate the VM to a database or file and restore it later. Check out the Concepts.
  • Run the scripts on your custom host API for your particular application
  • Execute out of non-addressable ROM (e.g. serial flash)

There are a few similar alternatives floating around but Microvium takes a unique approach (see Alternatives).


In the current design, a VM cannot exceed 64 kB of ROM and/or RAM since it internally uses 16-bit pointers.

There is no standard library and only a subset of JavaScript is currently supported.

The FFI (the interface to C) does not yet facilitate the passing of complex structures. Only simple types: string, int, double, and bool.


Microvium can be used in 3 ways:

  1. npm install -g microvium globally will install a CLI that runs microvium scripts (and by default produces a snapshot of the final state, in case you want to deploy it)

  2. npm install microvium will install Microvium as an npm library with TypeScript definitions. This is useful if you want to run Microvium on a custom node.js host and control the snapshotting and host API yourself.

  3. Integrate microvium.c into your C or C++ project to resume execution of a snapshot.

See Getting Started which walks you through all 3 of these.



Check out ./doc/


A compact, embeddable scripting engine for applications and microcontrollers for executing programs written in a subset of the JavaScript language.







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