‘Cannot find module’ error when package directory name ends with ‘next’

Explanation of the problem

The issue encountered is Next.js’ inability to locate a module in a package despite its existence, but only when the parent directory’s name ends with “next”. This problem occurs while attempting to create an npm package that other Next.js developers can import and use. The package’s name is “repro”, and it resides in a directory named “next” that has an “examples/basic” subdirectory, which is a Next.js application. The application relies on the package through a “npm install ../..” command, creating a “repro”: “file:../..” entry in its dependencies.

When running the examples/basic Next.js application, API routes fail to import code from the package and generate a module resolution error, as seen in the provided error message. This error occurs only if the parent directory is named “next” or has a name that ends with “next,” such as “foo-next.” However, it does not occur if the parent directory is named something else, such as “foo” or “next-foo.”

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Problem solution for ‘Cannot find module’ error when package directory name ends with ‘next’

Other popular problems with Next.js

<code class="language-javascript">import dynamic from 'next/dynamic';

const MyComponent = dynamic(() => import('../components/MyComponent'), {
  ssr: false
});

export default function Home() {
  return (
    <div>
      <MyComponent />
    </div>
  );
} 

This error occurs when a module tries to import the “fs” module, which is a built-in Node.js module that provides access to the file system, but is not available in the browser environment.

Solution:

To fix this issue, you can add the “webpack” property to the “next.config.js” file and set the “fs” module to “empty”. Here’s an example of how to do this:

module.exports = {
  webpack: (config, { isServer }) => {
    if (!isServer) {
      config.node = {
        fs: 'empty'
      };
    }
    return config;
  }
};

In this example, we’re checking if the code is being executed on the server or client, and setting the “fs” module to “empty” only on the client side, where it’s not needed.

Problem: Error “Module parse failed: Unexpected token”.

This error occurs when Webpack encounters an unexpected token while parsing a module, such as an unsupported syntax or a missing dependency.

Solution:

To fix this issue, you can add a “resolve” property to the “next.config.js” file and set the “extensions” property to include the file extensions of the modules you’re using. Here’s an example of how to do this:

  module.exports = {
    resolve: {
       extensions: ['.ts', '.tsx', '.js', '.jsx']
  }
};

Most popular use cases for Next.js

1. Server-side rendering and static site generation: Next.js allows developers to build applications that support server-side rendering (SSR) and static site generation (SSG) out of the box. This means that the server can pre-render pages and send them to the client as HTML, allowing for faster initial load times and improved SEO. To enable SSR or SSG, developers can use Next.js’s built-in functions such as getServerSideProps() or getStaticProps() to fetch data and generate pages at build time or request time.

Example code block for using getStaticProps():

export async function getStaticProps() {
  // Fetch data from an API or database
  const res = await fetch('https://api.example.com/data');
  const data = await res.json();

  // Return the data as props
  return {
    props: {
      data,
    },
  };
}

2. Automatic code splitting: Next.js automatically splits code into smaller chunks based on the routes of the application. This means that users only download the code they need for the current page, resulting in faster load times and better performance. Developers can also manually split code using dynamic imports and import statements with webpack’s code splitting features.

Example code block for manual code splitting:

import dynamic from 'next/dynamic';

const ComponentWithHeavyDependencies = dynamic(
  () => import('../components/ComponentWithHeavyDependencies'),
  { ssr: false }
);

function HomePage() {
  return (
    <div>
      <ComponentWithHeavyDependencies />
    </div>
  );
}

3. Fullstack development: Next.js can be used for fullstack development, allowing developers to build both the client and server-side of an application using a single language and framework. With features like API routes and serverless functions, developers can easily create backend logic to power their applications. Next.js also integrates with popular databases, such as MongoDB and PostgreSQL, and has support for authentication and authorization libraries like Passport.js and NextAuth.js.

Example code block for an API route:

export default function handler(req, res) {
  const data = { name: 'John', age: 30 };
  res.status(200).json(data);
}