next-learn/dynamic-routes-starter/lib/posts.js

import fs from 'fs'
import path from 'path'
import matter from 'gray-matter'

const postsDirectory = path.join(process.cwd(), 'posts')

export function getSortedPostsData() {
  // Get file names under /posts
  const fileNames = fs.readdirSync(postsDirectory)
  const allPostsData = fileNames.map(fileName => {
    // Remove ".md" from file name to get slug
    const slug = fileName.replace(/\.md$/, '')

    // Read markdown file as string
    const fullPath = path.join(postsDirectory, fileName)
    const fileContents = fs.readFileSync(fullPath, 'utf8')

    // Use gray-matter to parse the post metadata section
    const { data } = matter(fileContents)

    // Combine the data with the slug
    return {
      slug,
      ...data
    }
  })
  // Sort posts by date
  return allPostsData.sort((a, b) => {
    if (a.date < b.date) {
      return 1
    } else {
      return -1
    }
  })
}