React Uncaught ReferenceError: process is not defined

Upgrading to react-scripts v5 is not always the solution.

The full reason for this bug is described here. In short here is a brief summary:

The error is as a result of react-error-overlay (which many people would never have heard of because it is a dependency of react-scripts). This package's dependencies were update to support webpack v5, which unfortunately is not compatible with react-scripts v4.

Method 1

If upgrading to react-scripts v5 is not working for you, you can also try another workaround which is to pin react-error-overlay to version 6.0.9:

Delete your yarn.lock or package-lock.json, then install your dependencies again.

yarn

yarn will take the resolutions field into consideration out of the box.

"resolutions": {
  "//": "See https://github.com/facebook/create-react-app/issues/11773",
  "react-error-overlay": "6.0.9"
}

For yarn workspaces, place the above resolution in the root package.json, not in the problematic folder. See this issue comment.

npm (>=v8.3.0)

The equivalent of resolutions for npm is overrides.

"overrides": {
  "react-error-overlay": "6.0.9"
},

npm (<8.3.0)

You need to make sure npm uses the resolutions field when you run npm install. To automate the installation, see this answer

Method 2

Yet another (not so popular) workaround is to use a webpack plugin:

plugins:[
  new webpack.DefinePlugin({
      process: {env: {}}
  })
]

If you use craco (v6.3.0+), you just need to modify your craco.config.js file to add that plugin:

{
  ...
  webpack: {
    plugins: {
      add: [
        new webpack.DefinePlugin({
          process: {env: {}}
        })
      ]
    }
  }
}

For customize-cra users, see this answer or this github comment.

This last method is not popular because not many CRA users ever have to touch webpack directly to work with react.

I tried updating react-scripts to 5.0.0, but that didn't work.

Solution: -

• If you are using npm: -

npm i -D react-error-overlay@6.0.9

• If you are using yarn: -

yarn add -D react-error-overlay@6.0.9

Until a fix is final(maybe this PR), for anyone using npm(not yarn) the solution is this:

add to package.json:

"resolutions": {
    "react-error-overlay": "6.0.9"
},

"scripts":{
    "preinstall": "npx npm-force-resolutions",
    ....
},

"devDependencies":{
    "react-error-overlay": "6.0.9",
...
}

and then do an

npm install

Add this code in package.json

 "devDependencies": {
"react-error-overlay": "6.0.9"  },

After that run npm install command. It worked for me after 2 days of scrolling on the internet.

The issue was solved by updating react-scripts to 5.0.0

I found the best solution.

The problem is because you lose window.process variable when React hotloads, and process exists only on node, not the browser.

So you should inject it to browser when the app loads.

Add this line to App.js

useEffect(() => {
    window.process = {
      ...window.process,
    };
  }, []);

A lot of answers suggest overriding the react-error-overlay to 6.0.9, but this didn't work for me (on February 11th, 2022). I was using react-scripts 5.0.0 and react-error-overlay 6.0.10 before trying out the overlay override.

Instead of going through the hastle of defining the webpack configuration in my CRA application (as suggested by smac89), I downgraded react-scripts to 4.0.3.

It works fine with react-scripts: 4.0.3, which resolved react-error-overlay to 6.0.10.

So, my fix is:

• Set "react-scripts": "4.0.3" in package.json
• Delete your lock file (yarn.lock or package-lock.json) and node_modules
• Run install

For those still having issues with this: If using Webpack, run npm install -D dotenv-webpack and if using typescript npm install -D @types/dotenv-webpack.
Then in your Webpack config, add import Dotenv from "dotenv-webpack"; And

...
plugins: [
    ...
    new Dotenv(),
],
...

See https://github.com/mrsteele/dotenv-webpack/blob/master/README.md

After trying everything else, this finally worked for me.

The only solution that worked for me was a modification of what @smac89 wrote for craco. First add process as a dependency.

yarn add process or npm i process

Then add these lines to your craco.config.js.

const webpack = require('webpack');

module.exports = {
webpack: {
     ...
     plugins: {
        add: [
            new webpack.ProvidePlugin({
                process: 'process/browser.js',
            }),
            new webpack.DefinePlugin({
                'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
            }),
        ],
      },
    },
};

This, in turn, doesn't show the below warning in the console every time you start the project.

WARNING in DefinePlugin Conflicting values for 'process.env'

Upgrading from react-scripts 4.0.3 to 5.0.0 Did not work for me. The only thing that finally worked is the above proposed solution

using yarn

  "devDependencies": {
        "react-error-overlay": "6.0.9"
      },
  "resolutions": {
        "react-error-overlay": "6.0.9"
      }

then yarn install

for npm i think "resolutions" has to be replaced by "overrides"

If you are using npm > v8.3 you can use overrides like so in your package.json.

  "overrides": {
    "react-error-overlay": "6.0.9"
  },

For more information about overrides, go here.

The issue is a breaking change in 6.0.10, some dependencies like react-dev-utils will install this version even if you pin the version of react-error-overlay to 6.0.9 that is why it is necessary to use overrides.

For these who are using create-react-app with customize-cra you can use the Method 2 solution from @smac89 with addWebpackPlugin, this works for me.

react-scripts: 5.0.0 webpack: 5.64.4

// config-overrides.js
const webpack = require('webpack');
const { override, addWebpackPlugin } = require('customize-cra');

module.exports = override(
  addWebpackPlugin(
    new webpack.DefinePlugin({
      process: { env: {} },
    })
  )
);

this solution throws a warning on npm start but the application compiles right.

WARNING in DefinePlugin
Conflicting values for 'process.env'

This warning didn't brake anything but if anyone knows how to fix it please answer this thread :)

in yarn.lock or package-lock.json file to find string

"react-error-overlay@npm:^6.0.9":
  version: 6.0.10 <-- here problem
  etc...

and replace to

react-error-overlay@^6.0.9:
  version "6.0.9"
  resolved "https://registry.yarnpkg.com/react-error-overlay/-/react-error-overlay-6.0.9.tgz#3c743010c9359608c375ecd6bc76f35d93995b0a"
  integrity sha512-nQTTcUu+ATDbrSD1BZHr5kgSD4oF8OFjxun8uAaL8RwPBacGBNPf/yAuVVdx17N8XNzRDMrZ9XcKZHCjPW+9ew==

saved file and run yarn install

Upgrading from react-scripts 4.0.3 to 5.0.0 worked for me.

I ended up with the following error (relevant if you're using craco):

TypeError: match.loader.options.plugins is not a function

This was solved by @weiwei in their answer here

Facing the same issue today (14th feb 22) using Docker containers for a ReactJS app and I solved it downgrading the react-scripts version to 4.0.3 and also installing react-error-overlay on version 6.0.9. So the steps were:

1. Remove the package-lock.json file
2. Into the package.json file
   1. Replace the dependency "react-scripts": "4.0.3"
   2. Add react-error-overlay into the dev dependencies with "react-error-overlay": "6.0.9"
3. Update npm: npm update

I hope it helps anybody to save some time, Cheers.

I had the same problem in reactJs and I fixed it with these steps:

Add to package.json:

1. "scripts": { "preinstall": "npx npm-force-resolutions" }
2. "resolutions": { "react-error-overlay": "6.0.9" }

Thanks, this works for me, as Kaleb was saying

if using Webpack, run npm install -D dotenv-webpack and if using typescript npm install -D @types/dotenv-webpack. Then in your Webpack config, add import Dotenv from "dotenv-webpack"; And

plugins: [
    ...
    new Dotenv(),
],

i just updated version of react-script now it works fine for me

  "dependencies": {    
    "react-scripts": "5.0.0",
  },

Moving to v5 of react scripts brought other issues for us, using the answer with the most votes also didn't work for us. Adding this to package.json did:

      "resolutions": {
    "react-error-overlay": "6.0.9"
  },
  "scripts": {
    "preinstall": "npx npm-force-resolutions",
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },

Note: This is a response to those who sees the process is not defined issue related to index.html, not the OP.

This might be due to that you are trying to use process.env directly in the index.html without using <% %>

Correct usage looks like this in index.html:

<% if (process.env.NODE_ENV !== 'production') { %>
  <script>
    /* Disable Google Analytics locally */
    window["ga-disable-G-something"] = true;
  </script>
<% } %>

Incorrect usage (which might be your issue):

<script>
if (process.env.NODE_ENV !== 'production') {
  /* Disable Google Analytics locally */
  window["ga-disable-G-something"] = true;
}
</script>

Upgrading react-scripts from v4 to "react-scripts": "^5.0.0", seem helped me