Dart Live

The Dart VM, compiled to WebAssembly, running in your browser, with stateful hot reload on the web.

Live: https://modulovalue.github.io/dart-live/

What this is

A single-page app, no server. The browser runs:

component	wasm size	role
dart_il.wasm	9.7 MB	Dart VM (emcc, ARM simulator)
dart_cfe.wasm	2.4 MB	Common front-end (dart2wasm), Dart to kernel
dart_analyzer.wasm	2.5 MB	Dart analyzer (dart2wasm)
vm_platform.dill	8.3 MB	Platform kernel (dart:core, dart:async, ...)
dart_sdk.sum	3.2 MB	Analyzer SDK summary

Total: about 26 MB uncompressed, 7.6 MB gzipped.

Pipeline

1. You type Dart in Monaco.
2. Browser JS calls dartCompile(source, vm_platform.dill), and the CFE wasm produces kernel bytes.
3. JS hands those bytes to dart_il_run, which has the VM wasm execute them through the ARM simulator.
4. print calls in Dart go through an EM_ASM bridge back to JS, which updates the DOM.
5. Run orphans the prior isolate and creates a fresh one, so state resets.
6. Hot Reload calls IsolateGroup::ReloadKernel in place. Top-level fields keep their values, but the library code is swapped to the new kernel.
7. Invoke (the inline CodeLens above every zero-arg top-level function) calls that function on the live isolate via Dart_Invoke, bypassing entry-point pragmas via --no-verify-entry-points.
8. Future.delayed actually waits wall-clock time. _embedderSleep forwards to emscripten_sleep via Asyncify, so the JS event loop stays responsive.
9. The analyzer runs in parallel against dart_sdk.sum and feeds Monaco via setModelMarkers.

Expert mode

The toggle in the toolbar reveals two extra CodeLens buttons above every top-level function:

• IL, a text dump of the unoptimized flow graph from Dart_CompileAll.
• IL Graph, the same flow graph rendered with @viz-js/viz, one Graphviz digraph per compiler phase, with phase tabs across the top.

Samples

Four starred samples exercise the headline feature (stateful hot reload plus invoke): iterative pi via the Leibniz series, Conway's Game of Life, bouncing 2D particles, and a counter. Hot Reload preserves the running state. Change the step batch, the gravity, the neighborhood rule, then press Hot Reload and keep going from where you were.

License

This repository contains a built artifact bundle. Build inputs and patches live in a separate working tree (Dart SDK plus an emcc-built embedder).