This is the index.js file for react web3 app.

index.js

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import reportWebVitals from './reportWebVitals';
import { Web3ReactProvider } from '@web3-react/core'
import Web3 from 'web3'

function getLibrary(provider) {
  return new Web3(provider)
}

ReactDOM.render(
  <React.StrictMode>
    <Web3ReactProvider getLibrary={getLibrary}>
    <App />
    </Web3ReactProvider>
  </React.StrictMode>,
  document.getElementById('root')
);
reportWebVitals();