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92 lines
3.5 KiB
Markdown
92 lines
3.5 KiB
Markdown
<!--
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name: 'Skill: Run browser-driven web app example'
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description: Example file for the Run app skill showing how to start a web dev server, drive it with chromium-cli, capture screenshots, and document app-specific gotchas
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ccVersion: 2.1.145
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-->
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# Example: Browser-driven web app
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You have a dev server that serves HTML to a browser. An agent in a
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headless container can't open a browser window — so "run the app" means
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launching the dev server, driving a headless Chromium against it, and
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producing a screenshot that proves the page rendered.
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Don't write a browser driver. Use `chromium-cli`.
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## Dev server
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Find the dev command (`package.json` `scripts.dev`, `Makefile`,
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README), start it in the background, and wait for it to actually serve:
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```bash
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npm run dev & # or yarn dev, pnpm dev, make serve, ./dev.sh
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echo $! > /tmp/dev.pid
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timeout 30 bash -c 'until curl -sf http://localhost:3000 >/dev/null; do sleep 1; done'
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```
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Don't `sleep 5` — poll the port. Stop with
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`kill $(cat /tmp/dev.pid)` (or `pkill -f 'npm run dev'`) before
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relaunching, or the next run hits `EADDRINUSE`.
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## Drive
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`chromium-cli` is a headless-Chromium REPL. Pipe a script to stdin:
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```bash
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chromium-cli --session app <<'EOF'
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nav http://localhost:3000
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wait-for text=Dashboard
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screenshot
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click button:has-text("New item")
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fill input[name="title"] Smoke test
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press Enter
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wait-for text=Smoke test
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screenshot
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console --errors
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EOF
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```
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Screenshots land in `chromium_cli/sessions/app/screenshots/` (latest
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symlinked as `screenshot.png`). That's the whole loop: `nav` →
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`wait-for` the element you need → act (`click` / `fill` / `type` /
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`press`) → `screenshot` → `console --errors` to check nothing threw.
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Full command reference: `chromium-cli` skill, or `help` at the prompt.
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For iterative debugging, run it under tmux and `send-keys` one command
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at a time — same commands, same session.
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**If `chromium-cli` isn't available:** adapt
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[electron.md](electron.md)'s REPL driver — the structure and commands
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transfer, but it's `_electron`-specific:
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import `{ chromium }` instead, launch with
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`chromium.launch({ args: ['--no-sandbox'] })`, acquire the page via
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`(await app.newContext()).newPage()` then `goto()` your dev URL, and
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drop the Electron-only window introspection
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(`.windows()`/`.firstWindow()`/the `windows` command).
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## What to put in the skill
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The project-specific bits only. `chromium-cli` handles the mechanics.
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- **Dev command + port + stop.** The exact start line, any env vars it
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needs, and the `kill`/`pkill` to stop it.
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- **Auth.** Whatever gets a logged-in session — a `set-cookie` line, a
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`fill`/`click` login sequence, or a helper script that does the API
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dance and emits the cookie.
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- **One representative interaction.** Not the whole app — one path that
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proves it's running, ending in a screenshot.
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- **App-specific gotchas.** Only the ones you actually hit.
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## Gotchas that recur
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- **React controlled inputs.** `eval el.value = '…'` doesn't fire
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React's onChange. Use `fill` / `type` — they go through Playwright's
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input pipeline.
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- **Websockets / long-poll.** `wait-idle` never settles. `wait-for` the
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element you actually need.
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- **Slow first paint.** Vite/Next compile routes on demand; the first
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`nav` can take 10s+. `wait-for` handles it; raw `sleep` doesn't.
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- **`screenshot-element <sel>`** crops to one element — use it when the
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diff is in a specific component, not the whole page.
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- **Check `console --errors` before declaring success.** A page can
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render its shell while every data fetch 500s.
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