嘿，我正在运行一个以express作为后端的angular2应用程序。遇到以下问题：

[3] Port 4200 is already in use. Use '--port' to specify a different port.
[3] [nodemon] app crashed - waiting for file changes before starting...
[1] [HPM] Error occurred while trying to proxy request /api/jobs from localhost:4200 to http://localhost:3000 (ECONNREFUSED) (https://nodejs.org/api/errors.html#errors_common_system_errors)

server.js:

import * as bodyParser from 'body-parser';
import * as dotenv from 'dotenv';
import * as express from 'express';
import * as morgan from 'morgan';
import * as mongoose from 'mongoose';
import * as path from 'path';

import setRoutes from './routes';

const app = express();
dotenv.load({path: '.env'});
app.set('port', (process.env.PORT || 3000));

app.use('/', express.static(path.join(__dirname, '../')));

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: false}));

app.use(morgan('dev'));

mongoose.connect(process.env.MONGODB_URI);
const db = mongoose.connection;
(<any>mongoose).Promise = global.Promise;

db.on('error', console.error.bind(console, 'connection error:'));
db.on('open', () => {
  console.log('Connected to MongoDB');
  setRoutes(app);

  app.get('/*', function (req, res) {
    res.sendFile(path.join(__dirname, '../index.html'));
  });

  app.listen(app.get('port'), () => {
    console.log('Angular 2 Full Stack listening on port ' + 
  app.get('port'));
  });
});

export {app};

• edit*：这里是孔代码。我想我没有达到db.on('open')的行

当我检查端口时：

我同时使用：使用此选项

"dev": "concurrently \"mongod\" \"ng serve -pc proxy.conf.json --open\" \"tsc -w -p server\" \"nodemon dist/server/server.js\"",