"Port 4200 is already in use. Use '--port' to specify a different port."

嘿，我正在使用Express作为后端运行Angular2应用程序。出现了以下问题：

[3] 端口4200已被占用。使用“--port”指定不同的端口。

[3] [nodemon] 应用程序崩溃 - 等待文件更改后再启动...

[1] [HPM] 尝试将来自localhost:4200的请求代理到http://localhost:3000时发生错误（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;
(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};

编辑：

这是整个代码。我认为我没有到达db.on('open')这一行。

当我检查端口时：

我使用concurrently：使用以下选项

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