$ npm install -g vue-cli
  $ vue init pwa my-project
  $ cd my-project
  $ npm install
  $ npm run dev

    
    self.addEventListener('fetch', event => {
      const { request } = event;
      const url = new URL(request.url);
    
      // Ignore not GET request or is is different origin.
      if (request.method !== 'GET' || url.origin !== self.location.origin) return;
    
      event.respondWith(async () => {
        try {
          // If not online and cache available then use cache
          if (!navigator.onLine) {
            const cache = await caches.match(request);
            if (cache) return cache;
          }
    
          // Request message
          const response = await self.fetch(request);
          
          // If not 'ok' then do not cache
          if (!response.ok) return response;
    
          // Add response to cache
          const openCache = await caches.open(CACHE_NAME);
          await openCache.put(request, response.clone());
    
          return response;
        } catch (error) {
          // User is landing on a page.
          return request.mode === 'navigate' ? caches.match('./') : '';
        }
      });
    });

    
    const socketIO = require('socket.io');
    const express = require('express');
    
    const app = express();
    const io = socketIO(app);
    

    app.post('/api/user', () => {
      io.emit('USER_COUNT_UPDATED');
    });

    
    app.get('/api/user/count', (req, res) => {
      res.json({ count: 99283374 }).end();
    });

    

    
    import io from 'socket.io-client';
    
    export default store => {
      const socket = io.connect();
    
      socket.on('connect', () => store.dispatch('app/connect'));
      socket.on('disconnect', () => store.dispatch('app/disconnect'));
    
      socket.on('USER_COUNT_UPDATED', () => store.dispatch('user/getCount'));
    };

    // Load Socket layer asynchronously in separate chunk
    import('./socket').then(socket => socket.default(store));
    
    // Setup service worker
    if ('serviceWorker' in navigator) {
      navigator.serviceWorker.register('service-worker.js', { scope: './' });
    }