Typescript 和 Express 中的错误处理 Node.js

Question

I'm starting with Node and Typescript and I have a question.

I have these 2 files.

server.ts

import express = require('express');
import IConfiguration from "../config/config";


export default class Server {

    public app: express.Application;
    public configuration: IConfiguration;

    constructor( configuration: IConfiguration ) {
        this.configuration = configuration;
        this.app = express();
    }

    static init(configuration: IConfiguration) {
        return new Server(configuration);
    }

    start(callback: Function) {
        this.app.listen(this.configuration.port, callback());
        this.app.use(express.static(this.configuration.public_path))
    }
}

index.ts

import Server from './server/server';
import Configuration from "./config/config";
import * as dotenv from 'dotenv';
import router from './router/router';

//Loading .env file
dotenv.config();

//Init config
const configuration = Configuration.init();

//Init server
const server = Server.init(configuration);
server.app.use(router);
server.start(() => {
   console.log('Server running at port ' + configuration.port);
});

In index.ts I have the app.listen callback on start function, but I dont know how write this error handling for capture the errors. How I can add this.on("error") on my callback function?

server.start(() => {
   console.log('Listening on port: ', port);
}).on('error', (e) => {
   console.log('Error happened: ', e.message)
});

I have tried put this in my index.ts but I get this error: "Property 'on' does not exist on type 'void'"

Answer 1

Your server variable is an instance of your Server class and when you call start it does not return anything, it just implicitly returns undefined (or void in Typescript terms) and undefined surely does not have on method, so you cannot chain it like that. This is what error message says, basically.

What you can do is return this.app from start method, for example.

    start(callback: Function) {
        this.app.listen(this.configuration.port, callback());
        this.app.use(express.static(this.configuration.public_path))
        return this.app;
    }

Or separate this two line like this:

server.start(() => {
   console.log('Listening on port: ', port);
});

server.app.on('error', (e) => {
   console.log('Error happened: ', e.message)
});

Answer 2

you cannot pass "err" to app.listen in express. I think you guys are confusing with http server:

const http = require('http'); const server = http.createServer(app);

server.on('error', (err) => {
  if (err) {
    console.log(err);
  }
});
 
server.listen(PORT, () => {
  console.log('Running')
});