djs

djs is a small JavaScript and TypeScript engine written in no_std Rust and built mainly for wasm32. It runs codemode scripts, model-written programs that call tools, process their results and return data, and replaces QuickJS in pi's codemode.

• One arena. All VM state lives in one byte array addressed by u32 offsets, so a new VM is a copy of a prebuilt image and the host reads results straight out of it.
• Suspend anywhere. The interpreter never recurses on the Rust stack for JS calls; it can stop between any two instructions and resume, also inside callbacks, getters and async functions.
• Persistence as code. A run waiting on its tools can be written out as a continuation dump: a plain JavaScript program that recreates it.
• No AST. A single pass compiles to stack bytecode; TypeScript is erased while parsing.
• Deterministic. Clock, randomness and weak references come from the host; the same inputs give byte-identical heaps, natively and in wasm.

It behaves like QuickJS, down to error messages (dquickts, a QuickJS fork, is the test oracle), passes 39,325 of the 39,365 test262 tests in its active group, and the wasm module is 350 KB brotli-compressed.

Documentation: How djs works, the guide (source in docs/guide/).

Using it

npm install @earendil-works/djs

import { Sandbox } from "@earendil-works/djs";

const sb = await Sandbox.create({
  asyncFunctions: { search: (q) => mySearch(q as string) },
  memoryLimit: 64 << 20,
});
const n = await sb.runAsync("const hits = await search(q); return hits.length", { q: "djs" });

See js/README.md for the package and js/pi/vm.ts for pi's codemode adapter.

Building and testing

Needs stable Rust (edition 2024) with the wasm32-unknown-unknown target and rust-src, and node 22.6+. Oracle tests need dquickts' qjs ($DJS_QJS).

cargo build                                  # the workspace
cargo run -p djs-cli -- run file.js          # run a script (also: repl, disasm)
scripts/build-wasm.sh                        # the wasm module
cargo test                                   # unit and integration tests
cargo run -p djs-docs -- build               # the guide: target/docs-site/

TESTING.md covers test262, the differential corpus and the stress modes; scripts/gate.sh is what every change to main must pass.

Further reading

• ARCH.md: the architecture.
• TESTING.md: how djs is tested.
• docs/decisions.md: the decision log (docs/decisions-index.md by topic).
• AGENTS.md, work/README.md: how work is organized.