[React.js] 尝试导入错误：'./registerServiceWorker' 不包含默认导出（导入为 'registerServiceWorker'）

Question

I am trying to create a react app fetching pokemon API, but I've encountered the following issue that says Attempted import error: './registerServiceWorker' does not contain a default export (imported as 'registerServiceWorker'). but I do have a export default App; in my App.js file, here's my following content, not too sure what is the issue, help will be massively appreciated.

App.js

import React, { Component } from 'react';
import './styles/App.css';


class App extends Component {
  render() {
    return (
      <div className="App">
        hellohello
      </div>
    );
  }
}


export default App;

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './components/App';
import registerServiceWorker from './registerServiceWorker';

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

const isLocalhost = Boolean(
  window.location.hostname === 'localhost' ||
    // [::1] is the IPv6 localhost address.
    window.location.hostname === '[::1]' ||
    // 127.0.0.0/8 are considered localhost for IPv4.
    window.location.hostname.match(
      /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
    )
);

export function register(config) {
  if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {

    const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
    if (publicUrl.origin !== window.location.origin) {

      return;
    }

    window.addEventListener('load', () => {
      const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;

      if (isLocalhost) {
        checkValidServiceWorker(swUrl, config);


        navigator.serviceWorker.ready.then(() => {
          console.log(
            'This web app is being served cache-first by a service ' +
              'worker.'
          );
        });
      } else {
        registerValidSW(swUrl, config);
      }
    });
  }
}

function registerValidSW(swUrl, config) {
  navigator.serviceWorker
    .register(swUrl)
    .then(registration => {
      registration.onupdatefound = () => {
        const installingWorker = registration.installing;
        if (installingWorker == null) {
          return;
        }
        installingWorker.onstatechange = () => {
          if (installingWorker.state === 'installed') {
            if (navigator.serviceWorker.controller) {

              console.log(
                'New content is available and will be used when all ' +
                  'tabs for this page are closed.'
              );


              if (config && config.onUpdate) {
                config.onUpdate(registration);
              }
            } else {

              console.log('Content is cached for offline use.');


              if (config && config.onSuccess) {
                config.onSuccess(registration);
              }
            }
          }
        };
      };
    })
    .catch(error => {
      console.error('Error during service worker registration:', error);
    });
}

function checkValidServiceWorker(swUrl, config) {
  fetch(swUrl, {
    headers: { 'Service-Worker': 'script' }
  })
    .then(response => {
      const contentType = response.headers.get('content-type');
      if (
        response.status === 404 ||
        (contentType != null && contentType.indexOf('javascript') === -1)
      ) {
        navigator.serviceWorker.ready.then(registration => {
          registration.unregister().then(() => {
            window.location.reload();
          });
        });
      } else {
        registerValidSW(swUrl, config);
      }
    })
    .catch(() => {
      console.log(
        'No internet connection found. App is running in offline mode.'
      );
    });
}

export function unregister() {
  if ('serviceWorker' in navigator) {
    navigator.serviceWorker.ready.then(registration => {
      registration.unregister();
    });
  }
}

Answer 1

Your module does not have a default export. It has a named export register .

You can import it using the alias registerServiceWorker with:

import { register as registerServiceWorker } from './registerServiceWorker';