Javascript 显示错误参考错误的角度项目

我目前通过angular和pusher在这个项目上工作，并且已经发现了这个错误，无法前进并且卡住了，所以任何人都可以帮助。。。。 该项目是建立一个实时轮询应用程序，需要推送功能。ng serve命令没有给出任何错误，并在localhost:4200上托管该命令，但当我打开浏览器时，它显示空白页，并使用ctrl+shift+I打开浏览器控制台，它给出以下错误

core.js:6456 ERROR ReferenceError: Pusher is not defined
 at new PusherService (pusher.service.ts:8)
 at Object.PusherService_Factory [as factory] (pusher.service.ts:18)
 at R3Injector.hydrate (core.js:11412)
 at R3Injector.get (core.js:11232)
 at NgModuleRef$1.get (core.js:25328)
 at Object.get (core.js:25042)
 at lookupTokenUsingModuleInjector (core.js:3342)
 at getOrCreateInjectable (core.js:3454)
 at Module.ɵɵdirectiveInject (core.js:14704)
 at NodeInjectorFactory.AppComponent_Factory [as factory] (app.component.ts:11)

require('dotenv').config();
const express = require('express');
const bodyParser = require('body-parser');
const Pusher = require('pusher');
const app = express();
const port = process.env.PORT || 4000;
const pusher = new Pusher({
  appId: process.env.PUSHER_APP_ID,
  key: process.env.PUSHER_KEY,
  secret: process.env.PUSHER_SECRET,
  cluster: process.env.cluster,
  encrypted: true,
});
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use((req, res, next) => {
res.header('Access-Control-Allow-Origin', '*');
res.header(
'Access-Control-Allow-Headers',
'Origin, X-Requested-With, Content-Type, Accept'
);
next();
});
app.post('/vote', (req, res) => 
{
  const { body } = req;
  const { player } = body;
  pusher.trigger('vote-channel', 'vote', {
    player,
  });
  res.json({ player });
});

app.listen(port, () => {
  console.log(`Server started on port ${port}`);
});