Next 13 Starter Guide

This project is a template Next 13 project. It use Next 13.4 version.

The minimum required functions are implemented as a template project and the essentials are explained. This project also implement unit testing, End-to-End testing, and analyzing source code by SonarQube.

Create New Project

Run below command to create a new next 13 project.

npx create-next-app@latest

On installation, you'll see the following prompts:

Need to install the following packages:
  create-next-app@13.4.19
Ok to proceed? (y) y
√ What is your project named? ... next13-starter-guide
√ Would you like to use TypeScript? ... No / Yes
√ Would you like to use ESLint? ... No / Yes
√ Would you like to use Tailwind CSS? ... No / Yes
√ Would you like to use `src/` directory? ... No / Yes
√ Would you like to use App Router? (recommended) ... No / Yes
√ Would you like to customize the default import alias? ... No / Yes

After the prompts, create-next-app will create a folder with your project name and install the required dependencies.

Usage

npm run dev

You can access http://localhost:3000 to use this application.

Change source directory

To use the src directory, move the app Router folder or pages Router folder to src/app or src/pages respectively. If you're using Tailwind CSS, you'll need to add the /src prefix to the tailwind.config.ts file in the content section like below.

// tailwind.config.ts
const config: Config = {
  content: ['./src/**/*.{js,ts,jsx,tsx}'],
}
export default config

Enable app router

If you enable app router, add the following to next.config.js.

// next.config.js
/** @type {import('next').NextConfig} */
const nextConfig = {
  // add
  experimental: {
    appDir: true,
  },
}

module.exports = nextConfig

※If you are using Next 13.4 or later, there is no need to add it.

Prettier Setup

Run below command to install prettier.

npm install --save-dev prettier eslint-config-prettier

※Use eslint-config-prettier to make Prettier and ESLint play nice together.

Create configuration file

Create a .prettierrc file in the root of your project. Prettier uses cosmiconfig for configuration file support. This means you can configure Prettier via .prettierrc.

{
  "trailingComma": "all",
  "tabWidth": 2,
  "semi": false,
  "singleQuote": true,
  "jsxSingleQuote": true,
  "printWidth": 100
}

Ignoring Code

To exclude files from formatting, create a .prettierignore file in the root of your project.

# Ignore artifacts:
build
coverage

# Ignore all HTML files:
**/*.html

Edit eslint configuration file

Add prettier to .eslintrc.json in the extends section.

{
  "extends": ["next/core-web-vitals", "prettier"]
}

Edit package.json

Add the following to package.json in the scripts section. You can use the prettier command to run Prettier from the command line. For details https://prettier.io/docs/en/cli

{
  "scripts": {
    "format": "prettier . --write",
    "format-file-patterns": "prettier \"./src/**/*.{js,jsx,ts,tsx,json,css}\" --write",
    "format-ignore-path": "prettier . --write --ignore-path {any file}"
  }
}

ESLint Setup

ESLint do not show Typescript errors by default like below.

// foo.ts
const foo = '123'
x = 123
/*
$ npm run lint
> next lint
✔ No ESLint warnings or errors
*/

Install plugins

Install plugins to run ESLint with recommended rules on your TypeScript code.

npm install --save-dev  @typescript-eslint/parser @typescript-eslint/eslint-plugin

Edit eslint configuration file

Add the follwing to .eslintrc.json.

{
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended",
    "plugin:@typescript-eslint/recommended-requiring-type-checking",
    "next/core-web-vitals",
    "prettier"
  ],
  "parser": "@typescript-eslint/parser",
  "parserOptions":  {
    "project": "./tsconfig.json"
  }
}

Default Layout

A layout is UI that is shared between multiple pages. On navigation, layouts preserve state, remain interactive, and do not re-render.You can define a layout by default exporting a React component from a layout.tsx file in app directory like below.

// app/layout.tsx
export default function RootLayout({ children }: { children: React.ReactNode }) {
  return (
    <html lang='en'>
      <body>{children}</body>
    </html>
  )
}

Metadata API

Metadata API (Next 13.2 or later) allows you to define metadata (e.g. meta and link tags inside your HTML head element) for improved SEO and web shareability.It only supported in Server Components.

Static Metadata

To define static metadata, export a Metadata object from a layout.tsx or page.tsx file.

// layout.tsx / page.tsx
import type { Metadata } from 'next'

export const metadata: Metadata = {
  // For more supported options
  // https://nextjs.org/docs/app/api-reference/functions/generate-metadata#metadata-fields
  title: 'some title',
  description: 'some description',
}

export default function Page() {}

Dynamic Metadata

You can use generateMetadata function to fetch metadata that requires dynamic values (e.g. current route parameters, external data).

// page.tsx
import { Metadata } from 'next'

type Props = {
  params: { id: string }
  searchParams: { [key: string]: string | string[] | undefined }
}

export async function generateMetadata(
  { params, searchParams }: Props,
): Promise<Metadata> {
  // If file path is app/products/[id]/page.tsx, you can get id from params.id
  const id = params.id

  // get search param
  const keyword = searchParams.get('keyword')

  // fetch data
  const item = await fetch(`https://.../${id}`).then((res) => res.json())

  return {
    title: item.title,
    description: item.description,
  }
}
export default function Page({ params, searchParams }: Props) {}

Error Handling

You can catch unexpected errors using error.tsx like below.

// app/foo/error.tsx
'use client' // Error components must be Client Components

import { useEffect } from 'react'

export default function Error({error, reset}: {
  error: Error & { digest?: string }
  reset: () => void
}) {
  useEffect(() => {
    console.error(error)
  }, [error])

  return (
    <div>
      <h2>Something went wrong!</h2>
      <!-- Attempt to recover by trying to re-render the segment -->
      <button onClick={() => reset()}>Try again</button>
    </div>
  )
}

// app/foo/page.tsx
export default async function ErrorHandling() {
  const response = await fetch('https://jsonplaceholder.typicode.com/user')
  if (!response.ok) {
    throw new Error('Something went wrong')
  }

  return (
    <div>
      <h1>Error Handling</h1>
    </div>
  )
}

Loading Page

To show loading indicator before page rendering, use app/loading.tsx.

// app/loading.tsx.
export default function Loading() {
  return (
    <div>
      Loading...
    </div>
  )
}

// app/loading/page.tsx.
export default function Loading() {
  const sleep = (ms: number) => new Promise((res) => setTimeout(res, ms));
  await sleep(5000);

  return (
    <div>
      Check loading indicator.
    </div>
  )
}

Not Found Page

The notFound function allows you to render the not-found file within a route segment as well as inject a tag.

// app/not-found.tsx
import Link from 'next/link'

export default function NotFound() {
  return (
    <div>
      <h2>Not Found</h2>
      <Link href="/">Return Home</Link>
    </div>
  )
}

// app/notFound/page.tsx.
import { notFound } from 'next/navigation'

export default async function NotFound() {
  const item = await fetch('https://jsonplaceholder.typicode.com/posts/999').then((res) => res.json())
  if (!item || Object.keys(item).length === 0) {
    // go to app/not-found.tsx
    notFound()
  }

  return (
    <div>
      <h2>Not Found</h2>
    </div>
  )
}

Server Components

React Server Components allow you to write UI that can be rendered and optionally cached on the server.With Server Components, we're laying the foundations to build complex interfaces while reducing the amount of JavaScript sent to the client, enabling faster initial page loads.

Server Components features:

Rendering on the server (Javascript is not sent to the client)
Fetch data (async/await is available)
Access backend resources (directly)
Keep sensitive information on the server (access tokens, API keys, etc)
Keep large dependencies on the server / Reduce client-side JavaScript
Browser-only APIs, Event listeners (onClick(), onChange(), etc), Lifecycle Effects (useState(), useReducer(), useEffect(), etc) is not available

// app/serverComponents/page.tsx.
import { notFound } from 'next/navigation'

type TestResponse = {
  userId: string
  id: string
  title: string
  body: string
}

export default async function ServerComponents() {
  const posts = (await fetch(`https://jsonplaceholder.typicode.com/posts`).then((res) =>
    res.json(),
  )) as TestResponse[]
  if (posts.length == 0) {
    notFound()
  }

  return (
    <div>
      {posts.map((post) => (
        <div key={post.id}>
          <h3>{post.title}</h3>
          <p title={post.body}>{post.body}</p>
        </div>
      ))}
    </div>
  )
}

Client Components

Client Components allows you to write interactive UI that can be rendered on the client at request time. To use Client Components, you can add the React "use client" directive at the top of a file, above your imports.

Client Components features:

Rendering on the client (Javascript is executed in the browser)
Fetch data (use useState・useEffect・SWR・React-query insted of async/await)
Add interactivity and event listeners (onClick(), onChange(), etc)
Use State and Lifecycle Effects (useState(), useReducer(), useEffect(), etc)
Use browser-only APIs
Use custom hooks that depend on state, effects, or browser-only APIs
Use React Class components

// app/clientComponents/page.tsx.
'use client'

import { useEffect, useState } from 'react'

export default function Counter() {
  const [count, setCount] = useState(0)

  useEffect(() => {
    console.log('count', count)
  }, [count])

  const handleClick = () => {
    setCount(count + 1)
  }

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={handleClick}>Click</button>
    </div>
  )
}

Client-side data fetching with SWR

Next.js has created a React hook library for data fetching called SWR. It is highly recommended if you are fetching data on the client-side. It handles caching, revalidation, focus tracking, refetching on intervals, and more.

// app/swr/page.tsx.
'use client'

import axios, { AxiosResponse } from 'axios'
import useSWR from 'swr'

type TestResponse = {
  userId: string
  id: string
  title: string
  body: string
}

const fetcher = async (url: string) =>
  await axios.get(url).then((res: AxiosResponse<TestResponse[]>) => res.data)

export default function Swr() {
  const { data, error, isLoading } = useSWR<TestResponse[], Error>(
    'https://jsonplaceholder.typicode.com/posts',
    fetcher,
  )

  if (error) {
    return <div>Failed to load</div>
  }

  if (isLoading) {
    return <div>Loading...</div>
  }

  return (
    <div>
      {data && data.length ? (
        <div>
          {data.map((post) => (
            <div key={post.id}>
              <h3>{post.title}</h3>
              <p title={post.body}>{post.body}</p>
            </div>
          ))}
        </div>
      ) : (
        <h2>Not found</h2>
      )}
    </div>
  )
}

Route Handlers

If you need to fetch data in a client component, you can call a Route Handler from the client. Route Handlers execute on the server and return the data to the client. This is useful when you don't want to expose sensitive information to the client, such as API tokens. Route Handlers are only available inside the app directory. They are the equivalent of API Routes inside the pages directory meaning you do not need to use API Routes and Route Handlers together.

app
├── routeHandlers
│     └── page.tsx ← execute on the client
└── api
     └── routeHandlers
          └── route.ts ← execute on the server

// app/routeHandlers/page.tsx
'use client'

import axios, { AxiosResponse } from 'axios'
import useSWR from 'swr'
import { useState } from 'react'

type TestResponse = {
  userId: string
  id: string
  title: string
  body: string
}

type TestRequest = {
  url: string
  postId: string
}

const fetcher = async (request: TestRequest) =>
  await axios
    .post(request.url, { postId: request.postId })
    .then((res: AxiosResponse<TestResponse>) => res.data)

export default function RouteHandlers() {
  const [postId, setPostId] = useState('1')

  const { data, error, isLoading } = useSWR<TestResponse, Error>(
    ['/api/routeHandlers', postId],
    ([url, postId]: [url: string, postId: string]) => fetcher({ url, postId }),
  )

  const handleSubmit = (e: React.FormEvent<HTMLFormElement>) => {
    e.preventDefault()
    const targetElement = e.currentTarget?.postId as HTMLInputElement
    if (targetElement) {
      setPostId(targetElement.value)
    }
  }

  if (error) {
    return <div>Failed to load</div>
  }

  if (isLoading) {
    return <div>Loading...</div>
  }

  return (
    <div>
      <div>
        <form onSubmit={handleSubmit}>
          <input name='postId' type='number' required placeholder='enter postId' />
          <button>search</button>
        </form>
      </div>
      <div>
        {data && Object.keys(data).length !== 0 ? (
          <div>
            <div key={data.id}>
              <h3>{data.title}</h3>
              <p title={data.body}>{data.body}</p>
            </div>
          </div>
        ) : (
          <h2>Not found</h2>
        )}
      </div>
    </div>
  )
}

// app/api/routeHandlers/route.ts
import 'server-only'
import { NextRequest, NextResponse } from 'next/server'
import { z } from 'zod'

const userSchema = z.object({
  postId: z.string(),
})

type TestResponse = {
  userId: string
  id: string
  title: string
  body: string
}

export const POST = async (request: NextRequest) => {
  try {
    const result = userSchema.safeParse(await request.json())
    if (!result.success) {
      return NextResponse.json({}, { status: 400 })
    }

    const postId = result.data.postId.trim()
    const post = (await fetch(`https://jsonplaceholder.typicode.com/posts/${postId}`).then((res) =>
      res.json(),
    )) as TestResponse
    if (!post || Object.keys(post).length === 0) {
      return NextResponse.json({}, { status: 500 })
    }

    return NextResponse.json(post, { status: 200 })
  } catch (error) {
    return NextResponse.json({}, { status: 500 })
  }
}

Unit Testing with Vitest

Vitest Setup

npm install --save-dev vitest @testing-library/react happy-dom @vitejs/plugin-react

Collect coverage

npm install --save-dev @vitest/coverage-v8

Create vitest.config.ts in the root directory and add the following to vitest.config.ts.

// vitest.config.ts
import react from '@vitejs/plugin-react'
import path from 'path'
import { defineConfig } from 'vitest/config'

export default defineConfig({
  plugins: [react()],
  test: {
    globals: true,
    environment: 'happy-dom',
    setupFiles: './src/unit-test/setup.ts',
    coverage: {
      provider: 'v8',
      include: ['src/**/*.{tsx,js,ts}'],
      all: true,
      reporter: ['html', 'clover', 'text']
    },
    root: '.',
    reporters: ['verbose'],
    outputFile: 'test-report.xml'
  },
  resolve: {
    alias: {
      '@': path.resolve(__dirname, './src'),
      '~': path.resolve(__dirname, './src'),
    },
  },
})

Add the following to package.json in the scripts section.

{
  "scripts": {
    "test": "vitest --coverage",
  }
}

Client-Components unit testing

// clientComponets/page.tsx
'use client'

import { useState } from 'react'

export default function ClientComponents() {
  const [count, setCount] = useState(0)

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click</button>
    </div>
  )
}

// unit-test/clientComponets/page.test.tsx
import { render, fireEvent } from '@testing-library/react'
import { expect, test, describe } from 'vitest'
import ClientComponents from '@/app/clientComponents/page'

describe('unit testing clientComponents/page.tsx', () => {
  describe('initial display check', () => {
    test('should display the initial number', () => {
      // Arrange
      const { getByText } = render(<ClientComponents />)

      // Assert
      expect(getByText('You clicked 0 times')).toBeDefined()
    })
  })

  describe('test useState function', () => {
    test('should display the number of clicks', () => {
      // Arrange
      const { getByText } = render(<ClientComponents />)

      // Act
      fireEvent.click(getByText('Click'))

      // Assert
      expect(getByText('You clicked 1 times')).toBeDefined()
    })
  })
})

Server-Components unit testing

// serverComponets/page.tsx
import { notFound } from 'next/navigation'

export default async function ServerComponents() {
  const posts = await fetch(`https://jsonplaceholder.typicode.com/posts`).then((res) => res.json())
  if (!posts || posts.length == 0) {
    notFound()
  }

  return (
    <div>
      <h2>Post List</h2>
      {posts.map((post) => (
        <div key={post.id}>
          <h3>{post.title}</h3>
          <p title={post.body}>{post.body}</p>
        </div>
      ))}
    </div>
  )
}

// unit-test/serverComponets/page.test.tsx
import { render } from '@testing-library/react'
import { expect, test, describe, vi, afterEach } from 'vitest'
import ServerComponents from '@/app/serverComponents/page'

const notFoundMock = vi.hoisted(() => vi.fn())
const responseData = [
  {
    id: 1,
    title: 'test title 1',
    body: 'test body 1',
  },
  {
    id: 2,
    title: 'test title 2',
    body: 'test body 2',
  },
]

describe('unit testing serverComponents/page.tsx', () => {
  const response = {} as Response
  vi.mock('next/navigation', () => ({
    notFound: notFoundMock,
  }))

  afterEach(() => {
    vi.restoreAllMocks()
  })

  test('should display the post list', async () => {
    // Arrange
    response.json = vi.fn().mockResolvedValue(responseData)
    vi.spyOn(global, 'fetch').mockResolvedValue(response)
    const { getByText } = render(await ServerComponents())

    // Assert
    expect(getByText('test title 1')).toBeDefined()
    expect(getByText('test body 1')).toBeDefined()
    expect(getByText('test title 2')).toBeDefined()
    expect(getByText('test body 2')).toBeDefined()
    expect(notFoundMock).not.toBeCalled()
  })

  test('should call notFound function', async () => {
    // Arrange
    response.json = vi.fn().mockResolvedValue([])
    vi.spyOn(global, 'fetch').mockResolvedValue(response)
    render(await ServerComponents())

    // Assert
    expect(notFoundMock).toHaveBeenCalledOnce()
  })
})

End to End Testing with Puppeteer

End to end testing is a software testing technique that verifies the functionality and performance of an entire software application from start to finish by simulating user scenarios. Puppeteer is a NodeJS library that allows developers to programmatically control a web-browser.

Setup

npm install --save-dev puppeteer

Here is the page for the test. You can access it at localhost:3000/clientComponents

// clientComponents/page.tsx
'use client'

import { useState } from 'react'

export default function ClientComponents() {
  const [count, setCount] = useState(0)

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>Click</button>
    </div>
  )
}

Here is a sample End to End testing code. It tests submit button state.

// e2e-test/e2e.test.ts
import { afterAll, beforeAll, describe, expect, test } from 'vitest'
import { launch, PuppeteerLaunchOptions } from 'puppeteer'
import type { Browser, Page } from 'puppeteer'

// Set browser launch option. See the following for more details.
// https://pptr.dev/api/puppeteer.browserlaunchargumentoptions
const options: PuppeteerLaunchOptions = {
  headless: false,
  slowMo: 75,
  defaultViewport: {
    width: 1280,
    height: 1024,
  },
  devtools: true,
  args: ['--window-size=1680,1024'],
}

describe('End to End Testing', () => {
  let browser: Browser
  let page: Page

  beforeAll(async () => {
    browser = await launch(options)
    page = await browser.newPage()
  })

  afterAll(async () => {
    await browser.close()
  })

  test('If you click the submit button, should display the number of clicks', async () => {
    try {
      // Arrange
      await page.goto('http://localhost:3000/clientComponents')
      await page.screenshot({
        path: './src/e2e-test/before-click.png',
        fullPage: true,
      })
      const textBeforeClick = await page.$eval('p', (item) => {
        return item.textContent
      })

      // Act
      await page.click('button')
      await page.screenshot({
        path: './src/e2e-test/after-click.png',
        fullPage: true,
      })
      const textAfterClick = await page.$eval('p', (item) => {
        return item.textContent
      })

      // Assert
      expect(textBeforeClick).toBe('You clicked 0 times')
      expect(textAfterClick).toBe('You clicked 1 times')
    } catch (e) {
      console.error(e)
      expect(e).toBeUndefined()
    }
  }, 60000)
})

Add the following to scripts section in package.json.

{
  "scripts": {
    "test:e2e": "vitest --coverage --dir src/e2e-test",
  },
}

Run below command to run test.

# run application server
npm run dev

# run End to End testing
npm run test:e2e

Analyzing source code by SonarQube

SonarQube is a self-managed, automatic code review tool that systematically helps you deliver clean code.

# install SonarQube tools
npm install --save-dev sonarqube-scanner vitest-sonar-reporter

Add the following to vitest.config.ts.

add lcov to reporter section
add vitest-sonar-reporter to reporters section

// vitest.config.ts
import react from '@vitejs/plugin-react'
import path from 'path'
import { defineConfig } from 'vitest/config'

export default defineConfig({
  plugins: [react()],
  test: {
    globals: true,
    environment: 'happy-dom',
    setupFiles: './src/unit-test/setup.ts',
    coverage: {
      provider: 'v8',
      include: ['src/**/*.{tsx,js,ts}'],
      all: true,
      // add lcov
      reporter: ['html', 'clover', 'text', 'lcov']
    },
    root: '.',
    // add vitest-sonar-reporter
    reporters: ['verbose', 'vitest-sonar-reporter'],
    outputFile: 'test-report.xml'
  },
  resolve: {
    alias: {
      '@': path.resolve(__dirname, './src'),
      '~': path.resolve(__dirname, './src'),
    },
  },
})

Create sonar-project.properties in the root directory and add the following to sonar-project.properties. See this for more details.

sonar.projectKey=next13-starter-guide
sonar.projectName=next13-starter-guide
sonar.sources=src
sonar.tests=src/unit-test/
sonar.test.inclusions=src/unit-test/**/*.test.tsx
sonar.exclusions=**/*plugins*/**, src/unit-test/**/*.test.tsx, src/unit-test/**/setup.ts
sonar.testExecutionReportPaths=test-report.xml
sonar.javascript.file.suffixes=.js,.jsx
sonar.typescript.file.suffixes=.ts,.tsx
sonar.typescript.lcov.reportPaths=coverage/lcov.info
sonar.javascript.lcov.reportPaths=coverage/lcov.info
sonar.login=sqp_XXXXXXXXXXXXXXXXX

Create SonarQube project

Make sure you have installed SonarQube on your development machine. Run SonarQube server as localhost:9000 before do the following.

To create a SonarQube project, do the following.

Access the following url. http://localhost:9000/projects
Click [Create Project] and then click [Manually]
Input next13-starter-guide in Project display name and Project key. Click [Set Up]
Click [Locally]
Click [Generate] and then generate project token

Analyze your source code

Add project token to sonar.login in sonar-project.properties. See this for more details of token.

sonar.login=sqp_XXXXXXXXXXXXXXXXXXXXXX

Add the following to scripts section in package.json.

{
  "scripts": {
    "sonar": "sonar-scanner"
  },
}

Run below command to run SonarQube analysis.

# run all tests
npm run test

# run SonarQube analysis
npm run sonar

You can access the following url to show result.

http://localhost:9000/dashboard?id=next13-starter-guide

Name		Name	Last commit message	Last commit date
Latest commit History 4 Commits
public		public
src		src
.eslintrc.json		.eslintrc.json
.gitignore		.gitignore
.prettierrc		.prettierrc
README-jp.md		README-jp.md
README.md		README.md
next.config.js		next.config.js
package-lock.json		package-lock.json
package.json		package.json
postcss.config.js		postcss.config.js
sonar-project.properties		sonar-project.properties
tailwind.config.ts		tailwind.config.ts
test-report.xml		test-report.xml
tsconfig.json		tsconfig.json
vitest.config.ts		vitest.config.ts

N-Laboratory/next13-starter-guide

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Next 13 Starter Guide

Contents

Create New Project

Usage

Change source directory

Enable app router

Prettier Setup

Create configuration file

Ignoring Code

Edit eslint configuration file

Edit package.json

ESLint Setup

Install plugins

Edit eslint configuration file

Default Layout

Static Metadata

Dynamic Metadata

Client-side data fetching with SWR

Unit Testing with Vitest

Vitest Setup

Collect coverage

Client-Components unit testing

Server-Components unit testing

End to End Testing with Puppeteer

Setup

Analyzing source code by SonarQube

Create SonarQube project

Analyze your source code

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