1, StrictMode

After creating the project through the create-react-app scaffolding, the project’s index.js code looks like this:

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root')
);

// If you want your app to work offline and load faster, you can change
// unregister() to register() below. Note this comes with some pitfalls.
// Learn more about service workers: https://bit.ly/CRA-PWA
serviceWorker.unregister();
Copy the code

StrictMode enables React StrictMode. This is different from what the application expects. About the introduction of strict mode can refer to the official document: zh-hans.reactjs.org/docs/strict…