Chapter 22: Jenkins Language Projects — Java to Python

22.9 Node.js — pointer to chapters 20 and 21

By Ravindra Bagale · Last updated: 25 October 2026

Why: the problem

Think of the Swiggy web team and the Instagram-style front ends many Indian startups build. Their apps are Node.js: an Express API or a React site. Chapters 20 and 21 already took a Node app from a Freestyle job to a full Jenkinsfile. So this lesson does not repeat those chapters. Instead it puts Node in the same five-stage shape as every other language here, so you can compare it side by side, and it adds the Node habits that matter most in CI: npm ci instead of npm install, a pinned Node version, a lint step, JUnit test reports and an npm cache. Use this lesson as the quick bridge, and go back to chapters 20 and 21 for the full story.

What we will build

You will create badge-node with Express and the built-in node test runner, run npm ci, lint and test, write the five-stage Jenkinsfile with a node Docker agent, publish JUnit results, and smoke test the API.

What: every term in plain English

• Node.js — JavaScript that runs on a server.
• npm — Node package manager. Reads package.json.
• package-lock.json — Exact library versions. Commit it.
• npm ci — Clean install exactly from the lock file. Use it in CI.
• node --test — Node built-in test runner, no extra library.
• Express — A small Node web framework.
• .nvmrc — A file that names the Node version.
• node_modules — Installed libraries. Never commit it.

How: step by step

1. Make the folder

   mkdir -p ~/devops-lab/ch22/badge-node/test && cd ~/devops-lab/ch22/badge-node && echo 20 > .nvmrc
   

   What it does: Pin Node 20.

   Output

   (no output)
   

2. Init

   npm init -y > /dev/null && npm install express@4.21.1
   

   What it does: Creates the lock file.

   Output

   added 65 packages in 2s
   

3. Add files

   badge.js, server.js, test/badge.test.js from Example 1
   

   What it does: Copy exactly.

   Output

   (no output)
   

4. Test

   node --test
   

   What it does: Built-in runner.

   Output

   # tests 3
   # pass 3
   # fail 0
   

5. Run

   node server.js & sleep 1; curl -s "localhost:3000/badge?points=55"; kill %1
   

   What it does: The API.

   Output

   {"points":55,"level":"silver"}
   

6. Clean install

   rm -rf node_modules && npm ci
   

   What it does: Exactly from the lock.

   Output

   added 65 packages in 1s
   

7. Read chapter 20 and 21

   Open chapter 20 (Freestyle) and 21 (Jenkinsfile)
   

   What it does: Full Node story.

   Output

   (reading)
   

Example 1: Node badge API and tests

Stack. Node.js 20, Express

Goal. Node badge API and tests.

badge.js

function level(points) {
  if (points >= 100) return "gold";
  if (points >= 50) return "silver";
  return "bronze";
}
module.exports = { level };

server.js

const express = require("express");
const { level } = require("./badge");
const app = express();
app.get("/health", (req, res) => res.json({ status: "UP" }));
app.get("/badge", (req, res) => {
  const points = Number(req.query.points || 0);
  res.json({ points, level: level(points) });
});
const port = process.env.PORT || 3000;
app.listen(port, () => console.log("badge-node on " + port));

test/badge.test.js

const test = require("node:test");
const assert = require("node:assert");
const { level } = require("../badge");

test("gold at 100", () => assert.strictEqual(level(100), "gold"));
test("silver at 50", () => assert.strictEqual(level(50), "silver"));
test("bronze at 0", () => assert.strictEqual(level(0), "bronze"));

What each line does

• module.exports — Share level with other files.
• process.env.PORT — Port from the environment, default 3000.
• node:test — Built into Node 20.
• strictEqual — Value and type must match.

Green output

# tests 3
# pass 3
# fail 0

Expected result. Same rule, now in JavaScript.

Example 2: Five-stage Jenkinsfile for Node

Stack. Jenkins, Docker, Node

Goal. Five-stage Jenkinsfile for Node.

Jenkinsfile

pipeline {
  agent { docker { image 'node:20-alpine'; args '-v npm-cache:/root/.npm' } }
  options { timestamps() }
  environment { PORT = '13000' }
  stages {
    stage('Checkout') { steps { checkout scm } }
    stage('Install')  { steps { sh 'npm ci' } }
    stage('Test')     { steps { sh 'node --test --test-reporter=junit --test-reporter-destination=junit.xml' } }
    stage('Smoke') {
      steps {
        sh 'node server.js > app.log 2>&1 & echo $! > app.pid; sleep 2'
        sh 'wget -qO- "localhost:$PORT/badge?points=120" | grep gold'
        sh 'kill $(cat app.pid)'
      }
    }
    stage('Package') { steps { sh 'npm pack' } }
  }
  post {
    always  { junit 'junit.xml' }
    success { archiveArtifacts '*.tgz' }
  }
}

What each line does

• node:20-alpine — Pinned Node, small image.
• npm-cache volume — Faster npm ci.
• --test-reporter=junit — JUnit XML for Jenkins.
• wget — Alpine has wget, not curl.
• npm pack — Makes a tgz of the app.

Green output

[Pipeline] stage (Test)
[Pipeline] stage (Smoke)
{"points":120,"level":"gold"}
Archiving artifacts
Finished: SUCCESS

Expected result. Node in the same shape as Java, .NET, PHP and Python.

Example 3: npm ci fails when the lock is out of date

Stack. npm

Goal. npm ci fails when the lock is out of date.

console

npm ERR! `npm ci` can only install packages when your package.json and package-lock.json are in sync.
npm ERR! Missing: express@4.21.1 from lock file

What each line does

• Cause — package.json changed but the lock was not committed.
• Fix — npm install locally, commit package-lock.json, push.

Green output

git add package-lock.json && git commit -qm "Update lock" && git push -q
Finished: SUCCESS

Expected result. npm ci protects you from silent version changes.

Example 4: Add a lint step with ESLint

Stack. ESLint

Goal. Add a lint step with ESLint.

commands

npm install -D eslint@9 @eslint/js@9
npx eslint .

eslint.config.js

const js = require("@eslint/js");
module.exports = [js.configs.recommended, { languageOptions: { sourceType: "commonjs", globals: { require: "readonly", module: "writable", process: "readonly", console: "readonly" } } }];

stage

stage('Lint') { steps { sh 'npx eslint .' } }

What each line does

• -D — Dev dependency only.
• recommended — Catches unused variables and typos.
• globals — Tell ESLint about Node names.

Green output

(no output means no problems)

Expected result. Lint runs in seconds and catches typos before tests.

Verify: did it work?

1. Lock committed

   git ls-files package-lock.json
   

   What it does: Needed by npm ci.

   Output

   package-lock.json
   

2. Node version

   node -v
   

   What it does: Matches .nvmrc.

   Output

   v20.17.0
   

3. Health

   curl -s localhost:3000/health
   

   What it does: Running.

   Output

   {"status":"UP"}
   

When it is red 1

npm ERR! code EUSAGE ... package.json and package-lock.json are in sync

Cause. Lock not updated.

Fix, step by step

1. npm install locally, commit the lock.

When it is red 2

Error: listen EADDRINUSE: address already in use :::3000

Cause. Old process still on the port.

Fix, step by step

1. Use PORT=13000 in CI and kill in cleanup.

When it is red 3

sh: curl: not found

Cause. Alpine image has no curl.

Fix, step by step

1. Use wget -qO-, or apk add curl.

When it is red 4

npm ERR! EACCES: permission denied, mkdir '/.npm'

Cause. Container user has no home.

Fix, step by step

1. Set HOME=/tmp or mount a cache folder it can write.

Cleanup

1. Clean

   rm -rf node_modules *.tgz junit.xml
   

   What it does: Fresh.

   Output

   (no output)
   

Practice tasks

Homework: try at home

Recap

• Node fits the same stages.
• Use npm ci and commit the lock.
• Pin the Node version.
• Publish JUnit XML.
• Chapters 20 and 21 have the full story.

FAQ

Can Jenkins build the Node app and a Java API in the same job?

Yes. Use two stages or two parallel branches, each with its own Docker agent image. Lesson 22.10 shows the parallel version for all six languages.

Why not just copy the folder with node_modules to the server?

Libraries built on your laptop may not match the server, and the folder is huge. Install on the target with npm ci, or ship an image.

Yarn or pnpm?

Fine; use their frozen-lockfile install in CI.

Jest or node --test?

Either. Jest is more common in older projects.

React apps?

Same: npm ci, npm test, npm run build, then copy the build folder or make an image.

Should node_modules be cached?

Cache ~/.npm, not node_modules.

Which Node version?

An LTS like 20 or 22, same as production.

Do I need PM2?

On a VM yes; in containers the container runtime restarts the app.

Interview questions

1. Why npm ci in CI?

   Exact, clean installs from the lock; fails if out of sync.

2. How do you report Node tests in Jenkins?

   JUnit reporter output plus the junit step.

3. How do you pin Node in CI?

   Docker image tag or .nvmrc with a tool installer.

4. What does EADDRINUSE mean?

   Port already in use.

5. What does npm pack make?

   A tgz of the package.

Samajla ka?

Ravi Sir's Cards for this lesson

Revision cardInterview card

मराठी cards