Next.js と MDX でブログを構築する方法

yarn create next-app nextjs-mdx-blog

const root = process.cwd()

import path from 'path'

const POSTS_PATH = path.join(root, 'data', 'blog') 
// 出力例：A:/nextjs-mdx-blog/data/blog

import fs from 'fs'

export const allSlugs = fs.readdirSync(POSTS_PATH)
// 出力例：['markdown.mdx', 'nextjs.mdx', 'react.mdx']

export const formatSlug = (slug) => slug.replace(/\.mdx$/, '')
/*
 * 例：formatSlug('markdown.mdx')
 * 出力：'markdown'
 */

export const getPostBySlug = async (slug) => {
  const postFilePath = path.join(POSTS_PATH, `${slug}.mdx`)
  // 出力例：A:/nextjs-mdx-blog/data/blog/slug.mdx
  const source = fs.readFileSync(postFilePath)
  // ファイルの内容を返す

  const { content, data } = matter(source)
  /*
   * 例：
   *  ---
   *  title: Hello
   *  slug: home
   *  ---
   *  <h1>Hello world!</h1>
   *
   * 戻り値：
   *  {
   *    content: '<h1>Hello world!</h1>',
   *    data: {
   *      title: 'Hello',
   *      slug: 'home'
   *    }
   *  }
   */

  const mdxSource = await serialize(content)
  // コンテンツを serialize (next-mdx-remote) で処理する

  const frontMatter = {
    ...data,
    slug,
  }
  // 後で使用するためにスラッグをフロントマターにも追加する

  return {
    source: mdxSource,
    frontMatter,
  }
}

export const getAllPosts = () => {
  const frontMatter = []

  allSlugs.forEach((slug) => {
    const source = fs.readFileSync(path.join(POSTS_PATH, slug), 'utf-8')

    const { data } = matter(source)

    frontMatter.push({
      ...data,
      slug: formatSlug(slug),
      date: new Date(data.date).toISOString(),
    })
  })

  return frontMatter.sort((a, b) => dateSortDesc(a.date, b.date))
}

// 日付の降順でソート
const dateSortDesc = (a, b) => {
  if (a > b) return -1
  if (a < b) return 1

  return 0
}

export const formatDate = (date) =>
  new Date(date).toLocaleDateString('en', {
    year: 'numeric',
    month: 'long',
    day: 'numeric',
  })
/*
 * formatDate('2022-08-21T00:00:00Z')
 * 出力：'August 21, 2022'
 */

import { formatDate } from '../lib/format-date'
import { getAllPosts } from '../lib/mdx'

import Link from 'next/link'

export default function Home({ posts }) {
  return (
    <>
      <h1 className='mb-8 text-6xl font-bold'>Blog</h1>
      <hr className='my-8' />
      <ul className='flex flex-col gap-3'>
        {posts.map(({ slug, title, summary, date }) => (
          <li key={slug}>
            <Link href={`/blog/${slug}`}>
              <a className='block rounded-lg border border-solid border-gray-300 p-6 shadow-md'>
                <div className='flex justify-between'>
                  <h2>{title}</h2>
                  <time dateTime={date}>{formatDate(date)}</time>
                </div>
                <p className='mt-4'>{summary}</p>
              </a>
            </Link>
          </li>
        ))}
      </ul>
    </>
  )
}

// getStaticProps ですべての記事を取得
export const getStaticProps = async () => {
  const posts = getAllPosts()

  return {
    props: {
      posts,
    },
  }
}

import { formatDate } from '../../lib/format-date'
import { allSlugs, formatSlug, getPostBySlug } from '../../lib/mdx'

import { MDXRemote } from 'next-mdx-remote'

export default function Blog({ post }) {
  const { title, date } = post.frontMatter

  return (
    <div>
      <h1 className='mb-2 text-6xl font-bold'>{title}</h1>
      <time dateTime={date} className='text-lg font-medium'>
        {formatDate(date)}
      </time>
      <hr className='my-8' />
      <article className='prose max-w-none'>
        <MDXRemote {...post.source} />
      </article>
    </div>
  )
}

export const getStaticProps = async ({ params }) => {
  const post = await getPostBySlug(params.slug)

  return {
    props: {
      post,
    },
  }
}

export const getStaticPaths = async () => {
  const paths = allSlugs.map((slug) => ({
    params: {
      slug: formatSlug(slug),
    },
  }))
  /*
   * paths の出力例：
   *   [
   *     { params: { slug: 'markdown' } },
   *     { params: { slug: 'nextjs' } },
   *     { params: { slug: 'react' } }
   *   ]
   */

  return {
    paths,
    fallback: false,
  }
}