Solving linter error no-undef for document

There are a number of ways to solve/get around this. The two key ways are to either specify document as global or to set the eslint-env as browser (what you probably want). You can do this 1) in-file, 2) in the configuration, or even 3) when running from the CLI.

1) In-file:

1. Set the environment as browser in your file:

   /* eslint-env browser */
   import React from 'react';
   import ReactDOM from 'react-dom';
   import App from './App';
   
   ReactDOM.render(
     <App />,
     document.getElementById('root'),
   );
   

2. Add it as a global in the file itself:

   /* global document */
   import React from 'react';
   import ReactDOM from 'react-dom';
   import App from './App';
   
   ReactDOM.render(
     <App />,
     document.getElementById('root'),
   );
   

2) In the eslint configuration:

1. Set the environment as browser in the configuration:

   {
     "env": {
       "browser": true,
       "node": true
     }
   }
   

2. Add it as a global in the configuration:

   {
     "globals": {
       "document": false
     }
   }
   

3) From the CLI:

1. Using env: eslint --env browser,node file.js

2. Using globals: eslint --global document file.js

Resources:
Specifying Globals with ESLint
Specifying Environments with ESLint
Specifying env with ESLint CLI
Specifying globals with ESLint CLI