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Luat in Your Browser: The Complete Engine Compiled to WebAssembly

· 4 min read
Senol Tas
Senol Tas
Founder & Principal Engineer, Maravilla Labs

Today we're excited to share something we've been working on for months: the complete Luat engine running in your browser via WebAssembly.

The Challenge​

When we started building documentation for Luat, we wanted more than static code examples. We wanted developers to experience Luat - to edit templates, see results instantly, and truly understand the power of Lua-powered templating.

The challenge? Luat is written in Rust and depends on the mlua crate, which binds to Lua's C implementation. This isn't your typical "compile to WASM" scenario.

The Solution: Emscripten + WebAssembly​

After weeks of experimentation, we successfully compiled the entire Luat stack to WebAssembly using Emscripten:

  • Lua VM - The complete Lua 5.4 runtime
  • mlua bindings - Rust-to-Lua bridge
  • Luat parser - Our Svelte-inspired template parser
  • Luat compiler - Template-to-Lua bytecode compilation
  • Luat engine - The complete rendering engine

The result? A ~2.5MB WASM bundle that runs the exact same code as the server-side Luat engine.

Interactive Documentation​

Every code example in our documentation is now interactive. Try it yourself - edit the code below and click "Run":

Loading Luat...

Click "Run" and watch your changes render instantly - no server roundtrip, no installation, no setup.

Powering the Landing Page​

Check out the See It In Action section on our homepage. Those aren't static code snippets - they're fully interactive playgrounds powered by the same WASM engine, compiling and rendering Luat templates right in your browser.

Technical Deep Dive​

For those curious about the implementation:

Memory Management​

We use Emscripten's memory management with a custom JavaScript wrapper that handles:

  • String passing between JS and WASM
  • Template caching in a thread-local engine instance
  • Proper cleanup to prevent memory leaks

Performance​

Despite running in the browser, performance is excellent:

  • Template compilation: under 1ms for multi-file projects
  • Rendering: around 2ms for typical templates with components
  • Initial WASM load: depends on network, but cached after first visit

Note: The playground runs Lua dynamically rather than compiling to bytecode ahead of time. In production server environments, Luat pre-compiles templates to Lua bytecode for even faster execution.

What This Means for You​

  1. Try Before You Install - Experience Luat without any setup
  2. Learn Interactively - Modify examples and see results instantly
  3. Share Snippets - Soon: shareable playground links
  4. Offline Documentation - The playground works offline once cached

Our Journey​

This wasn't easy. We spent countless hours debugging Emscripten configurations, wrestling with memory alignment issues, and optimizing bundle size. But seeing Luat run in the browser - the same engine that powers production applications - makes it all worth it.

This is what we love about building Luat: pushing boundaries and making powerful tools accessible to everyone.

Try It Now​

Head to our documentation and start playing with the interactive examples. No installation required - just your curiosity.

Questions about the WASM implementation? Reach out @thelabertasch on X.