How to avoid React loading twice with Webpack when developing

Question

Given the following directory structure:

my-project
|
|-- node_modules
    |
    |-- react
    |-- module-x
        |
        |--node_modules
            |
            |--react

You can see both my-project and module-x require React. I have the same problem as described on this question, but the suggestion is to remove react from the package.json dependencies. I do that and it works fine, as long as no node_modules are installed in module-x, because Webpack will use React from my-project. But if I'm in the process of developing module-x and the node_modules are installed, Webpack uses React from both my-project and module-x.

Is there a way I could have Webpack make sure only one instance of React is used, even though it's required on two separate levels?

I know I could keep module-x in a separate directory when developing, but it seems like I'd have to publish it and then install it in my-project to test it, and that's not very efficient. I thought about npm link, but had no luck with it since it still has node_modules installed in module-x.

This here sounds a lot like the same challenge I'm having, but it doesn't seem like npm dedupe or Webpack's dedupe option would work. I'm probably not understanding some important detail.

Answer 1

This issue usually arises when using npm link. A linked module will resolve its dependencies in its own module tree, which is different from the one of the module that required it. As such, the npm link command installs peerDependencies as well as dependencies.

You can use resolve.alias to force require('react') to resolve to your local version of React.

resolve: {
  alias: {
    react: path.resolve('./node_modules/react'),
  },
},

Answer 2

If you don’t want to (or can’t) modify the project configuration, there is a more straightforward solution: just npm link React itself back to your project:

# link the component
cd my-app
npm link ../my-react-component

# link its copy of React back to the app's React
cd ../my-react-component
npm link ../my-app/node_modules/react

Answer 3

Just in case it's useful for others, the solutions suggested above didn't work for me, I had to perform the following steps to solve it:

In the library:

1. Setup the libraries that are generating issues as peerDependencies in the package.json instead of dependencies or devDependencies, e.g. in my case react:

"peerDependencies": {
  "react": "^16.8.6",
  ...
}

2. run npm install
3. build the library (in my case, with a rollup -c npm script

In my main app:

4. change the version of my library to point to my local project with a relative path in package.json, e.g.

"dependencies": {
  "my-library": "file:../../libraries/my-library",
  ...
}

5. Add resolve.symlinks = false to my main app's webpack configuration

6. Add --preserve-symlinks-main and --preserve-symlinks to my package.json start script, e.g:

"scripts": {
  "build": "set WEBPACK_CONFIG_FILE=all&& webpack",
  "start": "set WEBPACK_CONFIG_FILE=all&& webpack && node --preserve-symlinks-main --preserve-symlinks dist/server.js",
}

7. run npm install
8. run npm run start