Transpile untranspiled modules from node_modules. Makes it easy to have local libraries and keep a slick, manageable dev experience.

npm install --save @weco/next-plugin-transpile-modules

or

yarn add @weco/next-plugin-transpile-modules

Classic:

// next.config.js
const withTM = require('@weco/next-plugin-transpile-modules');

module.exports = withTM({
  transpileModules: ['somemodule', 'and-another']
});

note: please declare withTM as your last plugin (the "most nested" one).

Example with next-typescript:

const withTypescript = require('@zeit/next-typescript');
const withTM = require('@weco/next-plugin-transpile-modules');

module.exports = withTypescript(
  withTM({
    transpileModules: ['somemodule', 'and-another']
  })
);

With next-compose-plugins:

const withPlugins = require('next-compose-plugins');

const withTypescript = require('@zeit/next-typescript');
const withTM = require('@weco/next-plugin-transpile-modules');

module.exports = withPlugins([
  [withTM, {
    transpileModules: ['some-module', 'and-another'],
  }],
  withTypescript,
], {
  // ...
});

Next.js 7 introduced Webpack 4 and Babel 7, which changed a couple of things, especially for TypeScript and Flow plugins.

If you have a transpilation error when loading a page, check that your babel.config.js is up to date and valid, you may have forgotten a preset there.

If you get a transpilation error when using Yarn workspaces, make sure you are using a babel.config.js and not a .babelrc. The former is a project-wide Babel configuration, when the latter works for relative paths only (and won't work as Yarn install dependencies in a parent directory).

If you add a local library (let's say with yarn add ../some-shared-module), Yarn will copy those files by default, instead of symlinking them. So your changes to the initial folder won't be copied to your Next.js node_modules directory.

You can go back to npm, or use Yarn workspaces. See an example in the official Next.js repo.

Lerna's purpose is to publish different packages from a monorepo, it does not help for and does not intend to help local development with local modules.

This is not coming from me, but from Lerna's maintainer.

So you are probably using it wrong, and I advice you to use npm or Yarn workspaces instead.

You may need to tell your Webpack configuration how to properly resolve your scoped packages, as they won't be installed in your Next.js directory, but the root of your Lerna setup.

const withTM = require('@weco/next--plugin-transpile-modules');

module.exports = withTM({
  transpileModules: ['@your-project/shared', '@your-project/styleguide'],
  webpack: (config, options) => {
    config.resolve.alias = {
      ...config.resolve.alias,
      // Will make webpack look for these modules in parent directories
      '@your-project/shared': require.resolve('@your-project/shared'),
      '@your-project/styleguide': require.resolve('@your-project/styleguide'),
      // ...
    };
    return config;
  },
});