@wasmer/sdk2

Run Wasmer packages in Node.js or the browser with one package-first sandbox API. The runtime is Wasmer + WASIX compiled to WebAssembly with wasm-bindgen; Node.js does not load a native addon.

@wasmer/sdk2 is the temporary package name for the next Wasmer JavaScript SDK.

Install

npm install @wasmer/sdk2

Run Python from Node.js

import { Wasmer } from "@wasmer/sdk2/node";

const wasmer = new Wasmer();
const sandbox = await wasmer.sandboxes.create({
  packages: ["python/[email protected]"],
  files: {
    "main.py": "print(sum(number * number for number in range(10)))",
  },
});

const output = await sandbox
  .command("python", ["/workspace/main.py"])
  .run();

console.log(output.text());

new Wasmer() is synchronous. Package downloads, sandbox creation, commands, and shutdown are asynchronous.

run() throws ProcessExitError for a non-zero exit, termination, or timeout by default. Pass { check: false } when the outcome is expected and should be inspected as an Output.

For live processes, use spawn() and iterate the SDK streams directly:

const process = await sandbox
  .command("python", ["-u", "-c", "print('ready')"])
  .spawn({ stdin: "pipe", stdout: "pipe", stderr: "capture" });

for await (const line of process.stdout.lines()) {
  console.log(line);
}

const result = await process.wait({ check: true });

Unlike run(), process.wait() is unchecked by default.

Call sandbox.close() and wasmer.close() when a long-lived application no longer needs them.

Node.js networking and caching

Use network: { mode: "host" } when a package needs TCP or DNS:

const sandbox = await wasmer.sandboxes.create({
  packages: ["wasmer/[email protected]"],
  network: { mode: "host" },
});

Node.js maps WASIX networking to node:net and node:dns. Its default .wasmer cache uses the same registry and package layout as the Rust and Python SDKs:

const wasmer = new Wasmer({
  cache: { directory: ".cache/wasmer" },
});

Compiled WebAssembly engine artifacts are intentionally not shared with native targets.

Browser

Import the browser entrypoint:

import { Wasmer } from "@wasmer/sdk2/browser";

const wasmer = new Wasmer();
const sandbox = await wasmer.sandboxes.create({
  packages: ["python/[email protected]"],
});
const output = await sandbox
  .command("python", ["-c", "print('Hello from the browser')"])
  .run();

Worker-backed WASIX execution requires a cross-origin-isolated page so the browser can use SharedArrayBuffer. Serve the page with Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: require-corp.

Browser package data is persisted with browser storage rather than the Node filesystem cache.

Examples

Run these from the repository root after npm run build in js/:

node js/examples/python.mjs
node js/examples/multiple_runtimes.mjs
node js/examples/edgejs_http.mjs
node js/examples/postgres_psql.mjs

The PostgreSQL example requires psql on PATH; set PSQL or pass its path as the first argument otherwise. All examples reuse the programs in ../fixtures/.

Build and test locally

Install Node.js 20 or newer, Rust nightly with rust-src, and the matching wasm-bindgen CLI:

rustup toolchain install nightly \
  --profile minimal \
  --component rust-src \
  --target wasm32-unknown-unknown
cargo +nightly install wasm-bindgen-cli --version 0.2.126 --locked

cd js
npm ci
npm run build
npm test

Run the network and browser regressions explicitly:

npm run test:edgejs
npm run test:postgres
npx playwright install chromium
npm run test:browser

npm run check type-checks the handwritten TypeScript API without rebuilding the wasm module.