Build a CI/CD Pipeline with GitHub Actions (Step by Step)

mkdir cicd-demo
cd cicd-demo
npm init -y
npm install --save-dev eslint prettier jest @babel/preset-env

// src/index.js
function add(a, b) {
  return a + b;
}

function divide(a, b) {
  if (b === 0) {
    throw new Error("Division by zero");
  }
  return a / b;
}

module.exports = { add, divide };

// src/__tests__/index.test.js
const { add, divide } = require("../index");

describe("add", () => {
  test("adds positive numbers", () => {
    expect(add(2, 3)).toBe(5);
  });

  test("adds negative numbers", () => {
    expect(add(-2, -3)).toBe(-5);
  });

  test("adds zero", () => {
    expect(add(5, 0)).toBe(5);
  });
});

describe("divide", () => {
  test("divides positive numbers", () => {
    expect(divide(10, 2)).toBe(5);
  });

  test("throws on division by zero", () => {
    expect(() => divide(5, 0)).toThrow("Division by zero");
  });

  test("divides negative numbers", () => {
    expect(divide(-10, 2)).toBe(-5);
  });
});

// .eslintrc.json
{
  "env": { "node": true, "es2022": true, "jest": true },
  "parserOptions": { "ecmaVersion": 2022 },
  "rules": {
    "no-unused-vars": "error",
    "no-undef": "error",
    "semi": ["error", "always"],
    "quotes": ["error", "double"],
    "no-console": "warn"
  }
}

// .prettierrc
{
  "semi": true,
  "singleQuote": false,
  "trailingComma": "all",
  "printWidth": 100,
  "tabWidth": 2
}

// jest.config.js
module.exports = {
  testEnvironment: "node",
  testMatch: ["**/__tests__/**/*.test.js"],
  collectCoverage: true,
  coverageDirectory: "coverage",
  coverageThreshold: {
    global: {
      branches: 80,
      functions: 80,
      lines: 80,
      statements: 80,
    },
  },
};

npx eslint src/
npx prettier --check src/
npx jest

# Dockerfile
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production

FROM node:20-alpine
WORKDIR /app
RUN addgroup -S appgroup && adduser -S appuser -G appgroup
COPY --from=builder /app/node_modules ./node_modules
COPY src/ ./src/
USER appuser
EXPOSE 3000
CMD ["node", "src/index.js"]

# Dockerfile.dev
FROM node:20-alpine
WORKDIR /app
RUN npm install -g nodemon
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["nodemon", "src/index.js"]

# .github/workflows/ci-cd.yml
name: CI/CD Pipeline

on:
  push:
    branches: [main, develop]
  pull_request:
    branches: [main]

env:
  NODE_VERSION: "20"
  DOCKER_IMAGE: your-dockerhub-username/cicd-demo

jobs:
  lint:
    name: Lint & Format Check
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: actions/setup-node@v4
        with:
          node-version: ${{ env.NODE_VERSION }}

      - name: Cache npm dependencies
        uses: actions/cache@v3
        id: npm-cache
        with:
          path: ~/.npm
          key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}
          restore-keys: |
            ${{ runner.os }}-node-

      - run: npm ci
      - run: npx eslint src/
      - run: npx prettier --check src/

  test:
    name: Test (Node ${{ matrix.node-version }})
    runs-on: ubuntu-latest
    needs: lint
    strategy:
      matrix:
        node-version: [18, 20, 22]
      fail-fast: false

    steps:
      - uses: actions/checkout@v4

      - uses: actions/setup-node@v4
        with:
          node-version: ${{ matrix.node-version }}

      - name: Cache npm dependencies
        uses: actions/cache@v3
        with:
          path: ~/.npm
          key: ${{ runner.os }}-node-${{ matrix.node-version }}-${{ hashFiles('**/package-lock.json') }}
          restore-keys: |
            ${{ runner.os }}-node-${{ matrix.node-version }}-
            ${{ runner.os }}-node-

      - run: npm ci
      - run: npx jest --coverage

      - name: Upload coverage report
        uses: actions/upload-artifact@v4
        if: ${{ matrix.node-version == env.NODE_VERSION }}
        with:
          name: coverage-report
          path: coverage/

  build:
    name: Build & Dockerize
    runs-on: ubuntu-latest
    needs: test
    if: github.ref == 'refs/heads/main'

    steps:
      - uses: actions/checkout@v4

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Log in to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_PASSWORD }}

      - name: Extract metadata for Docker
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.DOCKER_IMAGE }}
          tags: |
            type=sha,prefix=,suffix=,format=short
            type=ref,event=branch
            type=raw,value=latest,enable={{is_default_branch}}

      - name: Cache Docker layers
        uses: actions/cache@v3
        with:
          path: /tmp/.buildx-cache
          key: ${{ runner.os }}-buildx-${{ github.sha }}
          restore-keys: |
            ${{ runner.os }}-buildx-

      - name: Build and push Docker image
        uses: docker/build-push-action@v5
        with:
          context: .
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          cache-from: type=local,src=/tmp/.buildx-cache
          cache-to: type=local,dest=/tmp/.buildx-cache

  deploy:
    name: Deploy to Production
    runs-on: ubuntu-latest
    needs: build
    if: github.ref == 'refs/heads/main'

    steps:
      - uses: actions/checkout@v4

      - name: Deploy to Vercel
        uses: amondnet/vercel-action@v25
        with:
          vercel-token: ${{ secrets.VERCEL_TOKEN }}
          vercel-org-id: ${{ secrets.VERCEL_ORG_ID }}
          vercel-project-id: ${{ secrets.VERCEL_PROJECT_ID }}
          vercel-args: "--prod"

      - name: Notify deployment success
        run: |
          echo "✅ Deployed successfully!"
          echo "Commit: ${{ github.sha }}"
          echo "Branch: ${{ github.ref_name }}"

![CI/CD](https://github.com/yourusername/cicd-demo/actions/workflows/ci-cd.yml/badge.svg)