Can’t connect Express.js server to the Angular frontend - angularjs

Question

I created a Node.js application and also an Angular application. I need to get data from the database and also store data to the database. I'm having problems connecting my Express.js server to the Angular application.
File user.service.ts
import { Injectable } from '#angular/core';
import { Observable } from 'rxjs';
import { User } from '../User';
import { HttpClient, HttpHeaders } from '#angular/common/http';
import { BASE_URL } from '../const/config';
import { MONGO_EXPRESS_URL } from '../const/config';
#Injectable({
providedIn: 'root',
})
export class UserService {
constructor(private http: HttpClient) {}
getUsers(): Observable<User[]> {
return this.http.get<User[]>(`${MONGO_EXPRESS_URL}/fetchdata`);
}
}
File users.component.ts
import { Component, OnInit } from '#angular/core';
import { UserService } from 'src/app/services/user.service';
import { User } from '../../User';
#Component({
selector: 'app-users',
templateUrl: './users.component.html',
styleUrls: ['./users.component.css'],
})
export class UsersComponent implements OnInit {
users: User[] = [];
constructor(private userService: UserService) {}
ngOnInit(): void {
this.userService.getUsers().subscribe((users) => (this.users = users));
}
}
This error pops up when I run the Angular application:
File server.js
app.use("/", router);
app.listen(port, function () {
console.log("Server is running on Port: " + port);
});
router.route("/fetchdata").get(function (req, res) {
users.find({}, function (err, result) {
if (err) {
res.send(err);
} else {
res.send(result);
}
});
});

Answer 1

The problem is the route: https://localhost:4000.
It would be http://localhost:4000 (http:// instead of https://).

Answer 2

It should kind of look like this on your Node.js. You should set up the Express.js server like so:
constructor() {
this.app = express()
}
Initialize{
this.app.use((req, res, next) => {
res.header('Access-Control-Allow-Origin', '*');
res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept');
res.header('Access-Control-Allow-Methods', 'OPTIONS, GET, POST, PUT');
if('OPTIONS' === req.method){
res.sendStatus(200);
}
else {
next();
}
})
this.app.use(RouterWebservices)
this.app.listen(your.HttpPort, your.Ip, () => {
console.log('Server now listening at ', your.HttpPort, 'IP ', your.Ip);
})
}
Then you need to declare your variables in a router.webservice.ts file:
export const RouterWebservices = express.Router()
RouterWebservices.get('/fetchdata', FetchWebservice)
And write a FetchWebserivce where you simply answer the request with data.