Checkout, toolchain & lockfiles

Prepare a repeatable runner

Lesson 3 of 20 · 12 min · Module 1: Feedback and workflow structure

A new runner needs source, a runtime, and dependencies before application checks.

Free. No installation: you write and run the code in your browser, and it is checked automatically.

By the end, you’ll be able to…

Start from the repository contents
State the toolchain

The idea

A workflow combines an event boundary, job dependencies, and ordered steps. Conditions and prerequisite outcomes determine which jobs can run.

steps:
  - uses: actions/checkout@v4
  - uses: actions/setup-node@v4
    with: {node-version: "22"}
  - run: npm ci

01Start from the repository contents

actions/checkout retrieves the source associated with the run. A fresh runner does not automatically contain your project files.

02State the toolchain

setup-node chooses the Node version explicitly. Dependencies should be installed from a committed lockfile with npm ci.

03Check the sequence

The preparation steps must precede application commands. The practice model records the sequence; actual dependency execution happens on real Actions runners.

Your turn

Create the test job with checkout@v4, setup-node@v4 using node-version "22", npm ci, and npm test, in that order.

What the checks look for

Checks out source and selects Node 22
Installs before testing

Try it in the editor →

Take this with you

Make a fresh runner able to reproduce the preparation sequence.

Go a little further

Explain what happens when package.json and its lockfile disagree.