[Solved] Using `babel-preset-react-app` requires that you specify `NODE_ENV` or `BABEL_ENV` environment variables. Valid values are “development”, “test”, and “production”. Instead, received: undefined.

Running webpack gives the following error:


 The reason for the bug is:

The environment variable is not configured properly. Although the mode: ‘development’ configuration item is configured in webpack.dev.js, this environment variable is the environment variable for code running, not the environment variable for babel running, so it needs to be defined.


// Download cross-env. A library dedicated to defining environment variables 
npm install --save-dev cross- env

// Add the configuration in front of the webpage running command 
in package.json
 "scripts" : {
     "start": "npm run dev" ,
     "dev": " cross-env NODE_ENV=development webpack serve --config ./config /webpack.dev.js" 

Read More:

Leave a Reply

Your email address will not be published. Required fields are marked *