JavaLab is a Java 8/11/17 emulator that runs in the web. It only serves static files to users, so standing it up on a server requires little overhead. It's reminiscent of a bygone era, a time when icons had character, and the interface, even with its quirks, felt friendly and inviting.
Source of truth lives in three places - apps.json (the curated app manifest), templates/ (page HTML + the launcher/IDE JavaScript), and apps/<id>/ (each app's prebuilt jar, thumbnail, and any sources). The build pipeline compiles these into public/, which is the only directory served in production (static files behind nginx). Nothing in public/ is edited by hand - always rebuild.
All scripts live in scripts/ and are plain Node ESM (node scripts/<x>.mjs). The ones you run routinely are wrapped as npm run targets in package.json.
Run these (in order) after changing apps.json, a jar/thumbnail under apps/, or anything in templates/. The convenience wrapper npm run site runs all four back-to-back.
| Command | Script | What it does |
|---|---|---|
npm run build |
build.mjs |
Builds every app in apps.json into public/apps/<id>/. source:"local" compiles the app's .java with javac --release <javaTarget> and packages a runnable jar; source:"prebuilt" copies the committed jar. Also copies each thumbnail. Refuses javaTarget > 17 (the CheerpJ ceiling). |
npm run toolchain |
build-toolchain.mjs |
Builds the in-browser IDE toolchain into public/builder/: builder.jar (compile+jar builder), jlformat.jar (Format action), tools.jar (OpenJDK 8 javac), and gjf.jar (google-java-format). tools.jar is large + gitignored - it reuses public/spike/tools.jar if present, else downloads Temurin 8 and extracts lib/tools.jar. |
npm run bundle |
bundle.mjs |
esbuild-bundles the launcher (templates/main.js -> public/main.bundle.js) and the IDE (templates/ide/index.js -> public/ide.bundle.js + ide.bundle.css) into single minified IIFE files, so their asset URLs can be cache-busted. |
npm run generate |
generate.mjs |
Generates the static site from templates/ + apps.json: public/index.html (app data injected), per-app loader pages, and verbatim static assets. Appends ?v=<hash> to every CSS/JS/jar/thumbnail URL so Cloudflare's edge cache refetches after a rebuild. Run last. |
npm run site |
- | build && toolchain && bundle && generate - a full clean rebuild of public/. |
scripts/manifest.mjs is a shared helper (repo paths + apps.json loader) imported by the pipeline scripts; it is not run directly.
| Command | Script | What it does |
|---|---|---|
npm run serve |
serve.mjs |
Serves public/ at http://127.0.0.1:8088, mirroring nginx incl. HTTP Range (CheerpJ requires Range for jars). PORT= / VERBOSE=1 override. Preview only. |
| - | static-server.mjs |
The Range-capable static file server shared by serve.mjs and the e2e harnesses. Not run directly. |
| Command | Script | What it does |
|---|---|---|
npm run e2e |
e2e.mjs |
Full end-to-end check: launcher loads, gallery card renders + launches a real Swing app (asserted by pixels), "<- Gallery" teardown, .jar upload runs from IndexedDB, and - critically - verifies no network request ever carries jar bytes (privacy). Has an unconditional hard-deadline kill-switch. |
npm run verify:editor |
verify-editor.mjs |
Fast IDE-only check (no CheerpJ): editor<->state sync, New Simulation scaffold + modal, two-way file/class name sync, custom New/Rename/Delete modals, About modal. Fails if any native prompt/confirm/alert fires. |
npm run spike |
run-spike.mjs |
Drives the in-browser jdk.compiler spike harness across Java runtimes (node scripts/run-spike.mjs 17,11,8 ecj) and scrapes the pass/fail verdict. Has an unconditional global deadline that SIGKILLs wedged browsers (a hung CheerpJ renderer can otherwise outlive Playwright's own cleanup). Exit 0 if any runtime passes, 1 if none, 3 on the hard deadline. |
| Script | What it does |
|---|---|
scripts/smoke-live.mjs [url] |
Smoke-tests a deployed URL (default https://javalab.dconn.dev): loads it, launches the first gallery app, and confirms CheerpJ renders it over the wire. |
scripts/shot.mjs |
Screenshots the generated launcher + IDE for visual review (spike/shot-launcher.png, spike/shot-ide.png). |
nginx/javalab.conf is the production nginx server block (static public/ root, HTTP Range, cache headers). lib/ecj-3.26.0.jar is a bundled Eclipse compiler kept for the spike. devlog/ holds dated development notes.