---

THE 4-PIECE MAP YOU CAN RE-USE FOREVER

1. Trigger – when should it run?
2. Job – one unit of work (runs on a clean VM).
3. Step – a single command inside a job.
4. Artifact – pass files between jobs (optional).

Every workflow file is just:

name: whatever
on: { trigger }
jobs:
  job-id:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4   # always start with this
      - run:  any-shell-command
      - uses: any-pre-made-action@v1

---

WHAT WE DID, STEP-BY-STEP

Exercise 1 – “Hello World”
Trigger: every push
Job: 1 step that prints text.
Key point: the VM already has Ubuntu + bash; we only echoed.

Exercise 2 – Run Jest tests
Trigger: push / pull-request to main
Job: 4 steps

1. checkout (download your repo)
2. setup-node (install Node 22 + cache node_modules)
3. npm ci (clean install)
4. npm test (run Jest)
   Key point: setup-node with cache: npm saves ~30 s next run.

Exercise 3-A – Matrix
Same as Exercise 2, but we added:

strategy:
  matrix:
    node-version: [21, 22]

GitHub creates two identical jobs, one per value, and runs them in parallel.
You can matrix anything: OS, Python version, browser, etc.

Exercise 3-B – Pipeline (sequential + parallel)
We split work into four jobs and used needs: to enforce order:

lint → test-matrix → build → deploy
↑ (parallel) ↑ Only lint runs first; the two test jobs run side-by-side; build waits for both; deploy waits for build.
We also used actions/upload-artifact and download-artifact to pass the dist/ folder between jobs.

---

TINY TEMPLATES FOR YOUR NEXT PROJECT

A. Run tests on every PR (Node)

name: CI
on:
  pull_request:
    branches: [ main ]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 22
          cache: npm
      - run: npm ci
      - run: npm test

B. Matrix across Node versions

strategy:
  matrix:
    node: [18, 20, 22]

C. Pass files between jobs

# job 1
- uses: actions/upload-artifact@v4
  with:
    name: myfiles
    path: dist/

# job 2
- uses: actions/download-artifact@v4
  with:
    name: myfiles
    path: dist/

---

COMMON TRAPS YOU ALREADY MET

• Missing script – npm run lint → add the script in package.json.
• Linter picky – either fix the code or disable the rule; for labs, disabling is fine.
• YAML indentation – 2 spaces, never tabs.
• Forgot checkout – every job starts in an empty VM; always uses: actions/checkout@v4 first.

---

CHEAT-SHEET YOU CAN KEEP

need a Linux command?        →  run: <bash>
need Node?                   →  uses: actions/setup-node@v4
need Python?                 →  uses: actions/setup-python@v5
need to save files?          →  uses: actions/upload-artifact@v4
need to read them later?     →  uses: actions/download-artifact@v4
need secrets (API keys)?     →  ${{ secrets.YOUR_SECRET }}  (add in repo Settings → Secrets)

That’s it.