Could not find plugin "proposal-numeric-separator"

The following steps work:

1. Add the following line to package.json:

"resolutions": { 
  "@babel/preset-env": "7.5.5" 
},

2. Run the following command:

$ npx npm-force-resolutions

3. Install dependencies:

$ npm install
# or 
$ yarn

4. Build your project:

$ yarn build

Take a look at this Github Issue

From the corresponding issue in create-react-app,

Update react-scripts to 3.4.1 in your package.json file and remove node_modules as well as package-lock.json/yarn.lock and re-install.

Why this problem happened?:

It's an issue of conflicts between internal packages used by babel.

Adding a new plugin to @babel/compat-data breaks old @babel/preset-env versions. This is because preset-env iterates over compat-data's plugins, and throws if the plugin isn't defined in preset-env's available-plugins.js file.

This is the merge that fixed the issue: https://github.com/babel/babel/pull/11201/files/a88a00750c61ff89f1622d408d67108719f21ecd

Solution:

• Delete package-lock.json or yarn.lock
• Delete node_modules folder
• In package.jon I have adjusted the version numbers of these packages to:

    ...
    "devDependencies": {
        "@babel/compat-data": "^7.8.0",
        "@babel/preset-env": "^7.8.0",
        "babel-loader": "^8.1.0",
        ...
    },
    ...
    "resolutions": {
        "@babel/preset-env": "^7.8.0"
    }

• Run npm install
• Run npm run build

Try this, it works: npm i @babel/[email protected]

I have just used it like 10 minutes ago, and it's working fine.

Related issue going on github about this. Click Here!