How to avoid `loaded two copies of React` error when developing an external component?

Question

I am developing an external component (let's say my-component, which I link to the project with npm link (as it is in process and I need the package to reflect changes).

In the my-component folder there are node_modules/react and node_modules/react-dom as they are its dependencies. However they are peerDependences, so I did not suppose to bring them into the project linking this package.

However when using npm link, it link the whole directory, including node_modules. So, when the project builds, it includes packages 2 times: from node_modules/* and from node_modules/my-component/node_modules/*.

This begins to affect when the component is using ReactDOM.findDOMNode, it causes this error:

Warning: React can't find the root component node for data-reactid value `.0.2.0`. If you're seeing this message, it probably means that you've loaded two copies of React on the page. At this time, only a single copy of React can be loaded at a time.

Also, it may help to understand what's happening: the problem only appears if there are both node_modules/my-component/node_modules/react and node_modules/my-component/node_modules/react-dom. If there is only one of them, there is no error message.

The usual package installation does not bring such error as there is no node_modules/react-dom there.

How is it supposed to develop an external component and the project at the same time?

Answer 1

The issue is twofold:

1. You cannot have 2 copies of react loaded.
2. npm link creates a symlink, however the "require" doesnt respect the symlink and when it tries to navigate up the directory, it never finds the react of the parent project.

Solution:

All you have to do is link the react and react-dom in your component to that of parent project's node_modules folder.

Go to your component project and remove the react and react-dom then do

npm link ../myproject/node_modules/react
npm link ../myproject/node_modules/react-dom

Answer 2

Fixed it by adding react-dom as an alias to my webpack config

alias: {

    react$: require.resolve(path.join(constants.NODE_MODULES_DIR, 'react')),
    'react-dom': require.resolve(path.join(constants.NODE_MODULES_DIR, 'react-dom'))

}

Answer 3

Someone clevererer than I (@mojodna) came up with this solution: remove the duplicate dependencies from the external component, and resolve them with your project's copies of those deps.

Step 1: Remove the dependencies from your external component's node_modules

As @cleong noted, you can't just remove the deps from the external component's node_modules, because your project's build step will fail when it hits the now-missing dependencies in the external component.

Step 2: Add your project's node_modules to NODE_PATH

To fix this, you can append the project's node_modules to the NODE_PATH environment variable when running your build step. Something like e.g. this:

NODE_PATH=$(pwd)/node_modules/ npm start

(where npm start is your script that bundles your external component, via e.g. Browserify, Webpack, etc.)

In fact, you could always append that NODE_PATH addition to your build scripts, and it would work whether or not you've npm linked anything. (Makes me wonder if it shouldn't be default npm behavior...)

Note: I left my existing answer because there's some conversation there, and this is a different (and better) solution.