Next.js注释函数后仍出现Module Not Found错误原因咨询

跟随Next.js官方教程学习getStaticProps时，将getSortedPostsData()注释或改为字符串后，明明没使用这个模块，却依然出现无法从'fs'导入的错误。相关代码如下：

import Head from 'next/head';
import styles from '../styles/Home.module.css';
import Link from 'next/link';
import { getSortedPostsData } from '../lib/posts';
import Layout from '../components/layout'
import utilStyles from '../styles/utils.module.css';
export async function getStaticProps() {
  console.log("get static props runs")
  const allPostsData = 'getSortedPostsData();'
  return {
    props: {
      allPostsData,
    },
  };
}


export default function Home({ allPostsData }) {
  return (
    <Layout home>
    <div className={styles.container}>
      <Head>
        <title>Create Next App</title>
        <link rel="icon" href="/favicon.ico" />
      </Head>

      <main>
        <h1 className={styles.title}>
          Read <Link href="/posts/first-post">this page!</Link>
        </h1>

        <p className={styles.description}>
          Get started by editing <code>pages/index.js</code>
        </p>

        <div className={styles.grid}>
          <a href="https://nextjs.org/docs" className={styles.card}>
            <h3>Documentation &rarr;</h3>
            <p>Find in-depth information about Next.js features and API.</p>
          </a>

          <a href="https://nextjs.org/learn" className={styles.card}>
            <h3>Learn &rarr;</h3>
            <p>Learn about Next.js in an interactive course with quizzes!</p>
          </a>

          <a
            href="https://github.com/vercel/next.js/tree/master/examples"
            className={styles.card}
          >
            <h3>Examples &rarr;</h3>
            <p>Discover and deploy boilerplate example Next.js projects.</p>
          </a>

          <a
            href="https://vercel.com/import?filter=next.js&utm_source=create-next-app&utm_medium=default-template&utm_campaign=create-next-app"
            className={styles.card}
          >
            <h3>Deploy &rarr;</h3>
            <p>
              Instantly deploy your Next.js site to a public URL with Vercel.
            </p>
          </a>
        </div>
      </main>

      <footer>
        <a
          href="https://vercel.com?utm_source=create-next-app&utm_medium=default-template&utm_campaign=create-next-app"
          target="_blank"
          rel="noopener noreferrer"
        >
          Powered by{' '}
          <img src="/vercel.svg" alt="Vercel" className={styles.logo} />
        </a>
      </footer>

      <style jsx>{`
        main {
          padding: 5rem 0;
          flex: 1;
          display: flex;
          flex-direction: column;
          justify-content: center;
          align-items: center;
        }
        footer {
          width: 100%;
          height: 100px;
          border-top: 1px solid #eaeaea;
          display: flex;
          justify-content: center;
          align-items: center;
        }
        footer img {
          margin-left: 0.5rem;
        }
        footer a {
          display: flex;
          justify-content: center;
          align-items: center;
          text-decoration: none;
          color: inherit;
        }
        code {
          background: #fafafa;
          border-radius: 5px;
          padding: 0.75rem;
          font-size: 1.1rem;
          font-family: Menlo, Monaco, Lucida Console, Liberation Mono,
            DejaVu Sans Mono, Bitstream Vera Sans Mono, Courier New, monospace;
        }
      `}</style>

      <style jsx global>{`
        html,
        body {
          padding: 0;
          margin: 0;
          font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Roboto,
            Oxygen, Ubuntu, Cantarell, Fira Sans, Droid Sans, Helvetica Neue,
            sans-serif;
        }
        * {
          box-sizing: border-box;
        }
      `}</style>
    </div>
    <section className={`${utilStyles.headingMd} ${utilStyles.padding1px}`}>
        <h2 className={utilStyles.headingLg}>Blog</h2>
        <ul className={utilStyles.list}>
          {/* {allPostsData
          .map(({ id, date, title }) => (
            <li className={utilStyles.listItem} key={id}>
              {title}
              <br />
              {id}
              <br />
              {date}
            </li>
          ))} */}
          {console.log(`info: ${allPostsData}`)}
        </ul>
      </section>
    </Layout>
  )
}

原以为注释后未使用该模块就不会产生错误，请问这是为什么？

问题出在你依然保留了import { getSortedPostsData } from '../lib/posts';这行导入代码。

哪怕你没有调用getSortedPostsData函数，只要导入了../lib/posts模块，Node.js/Next.js就会加载并解析这个模块的全部内容——包括模块内部对fs模块的导入（官方教程里的posts.js正是用fs读取本地markdown文件的）。

fs是Node.js的核心模块，只能在服务器端环境使用。如果Next.js在不支持fs的环境下尝试加载该模块，就会抛出导入错误；即使是在服务器端执行的getStaticProps，只要模块被导入就会触发依赖解析，一旦posts.js里的fs导入在模块顶级作用域，就会被执行。

解决方法很简单：把那行导入getSortedPostsData的代码注释或删除，这样就不会加载包含fs依赖的posts模块，错误自然会消失。

内容的提问来源于stack exchange，提问作者PythonPadawan