Hi @giga Working example is given below.

SETUP

npm i socket.io-client --save
npm i @types/socket.io-client --save

Server-side (nodejs)

var express = require('express');
var path = require('path');
var app = express();
var server = require('http').Server(app);
var io = require('socket.io')(server);

var port = 8000;

app.use(express.static(path.join(__dirname, "public")));

io.on('connection', (socket) => {
console.log('new connection made');

socket.on('event1', (data) => {
  console.log(data.msg);
});

socket.emit('event2', {
  msg: 'Server to client, do you read me? Over.'
});

socket.on('event3', (data) => {
  console.log(data.msg);
  socket.emit('event4', {
    msg: 'Loud and clear :)'
  });
});
});

server.listen(port, () => {
  console.log("Listening on port " + port);
});

Client-side - Angular4 code

import { Component, OnInit } from '@angular/core';
import * as io from 'socket.io-client';

@Component({
    moduleId: module.id,
    selector: 'ch-home',
    styleUrls: ['home.styles.css'],
    templateUrl: 'home.template.html'
})

export class HomeComponent implements OnInit {
    messageText: string;
    messages: Array<any>;
    socket: SocketIOClient.Socket;

  constructor() {
   // this.socket = io.connect('http://localhost:8000');
   this.socket = io.connect();
  }

  ngOnInit() {
        this.messages = new Array();

        this.socket.on('message-received', (msg: any) => {
            this.messages.push(msg);
            console.log(msg);
            console.log(this.messages);
        });
      this.socket.emit('event1', {
          msg: 'Client to server, can you hear me server?'
      });
      this.socket.on('event2', (data: any) => {
        console.log(data.msg);
        this.socket.emit('event3', {
            msg: 'Yes, its working for me!!'
        });
      });
      this.socket.on('event4', (data: any) => {
          console.log(data.msg);
      });
   }

   sendMessage() {
    const message = {
      text: this.messageText
    };
    this.socket.emit('send-message', message);
    // console.log(message.text);
    this.messageText = '';
  }

}

Implement socket.io-client as an Angular service

Setup

npm install socket.io-client --save

Note (since Socket.IO v3):
Do not install @types/socket.io-client since the types are now included in the socket.io-client package. So you will face problems if you install them additionally (source).

The service:

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { io, Socket } from 'socket.io-client';

@Injectable()
export class ChatService {
  private socket: Socket;

  constructor() {
    this.socket = io('http://localhost:3000');
  }

  // EMITTER example
  sendMessage(msg: string) {
    this.socket.emit('sendMessage', { message: msg });
  }

  // HANDLER example
  onNewMessage() {
    return new Observable(observer => {
      this.socket.on('newMessage', msg => {
        observer.next(msg);
      });
    });
  }
}

In a component:

import { Component, OnInit } from '@angular/core';
import { ChatService } from './chat-service';

@Component({
  // ...blabla...
})
export class ChatComponent implements OnInit {
  msgInput: string = 'lorem ipsum';

  constructor(
    private chatService: ChatService,
  ) { }

  ngOnInit() {
    this.chatService.onNewMessage().subscribe(msg => {
      console.log('got a msg: ' + msg);
    });
  }

  sendButtonClick() {
    this.chatService.sendMessage(this.msgInput);
  }
}

Following the solution of @MA-Maddin, I did this implementation:

at Service:socket.service

import { Injectable } from '@angular/core';
import * as io from 'socket.io-client';
import {Observable} from 'rxjs';
@Injectable({
providedIn: 'root'
})
export class SocketService {
private socket:SocketIOClient.Socket;

constructor() { 
  this.socket=io('http://localhost:3300');
}
emit(event:string, data:any){
  this.socket.emit(event,data);
}
on(event:string){
  return Observable.create(observer=>{
   this.socket.on(event,data=>{
    observer.next(data);
   });
  })
 }
}

At Component

 import { Component, OnInit, Input, ViewChild, ViewEncapsulation} from 
'@angular/core';
import { AuthService } from 'src/app/auth/auth.service';
import Socket from '../../services/socket.service';

@Component({
  selector: 'app-lobby-chat',
  templateUrl: './lobby-chat.component.html',
  styleUrls: ['./lobby-chat.component.css'],
  encapsulation: ViewEncapsulation.None,
})
export class LobbyChatComponent implements OnInit {
  constructor(private socket:Socket) {
  this.socket.on('getMessage').subscribe(data=>{
  console.log(data);
  });
  }
  pushMessage(msg){
  this.socket.emit('sendMessage',msg);
  }
}

This will update your bindings correctly. Note: **use npm i "@types/socket.io-client for use or define Socket io Types **

I know its an old question , For me none of the solutions worked so I solved with below approach.

Do Not Waste your time if your socket connection polling is working fine and not getting any error , It might be due to the socket.io.client package conflict with your other setup

my application version are below.

Angular 12.x Socket.io.client 4.x Node 14.16.1 I also tried with ngx-socket-io package too that also didn't work. the strange part is socket.io poling works well hand shaking are correct but not able to listen the event on new messages.

So my final approach is adding socket.io manully to index.html of angular and dispatch and event to the compoent.

function RsCustomEvent ( event, message ) {
    params = { bubbles: false, cancelable: false, detail: message };
    var evt = document.createEvent( 'CustomEvent' );
    evt.initCustomEvent( event, params.bubbles, params.cancelable, params.detail );
    return evt;
}
var socket = io('localhost:3000');
socket.on("channel-name", function (message) {
    window.dispatchEvent(RsCustomEvent('socketEventListen',message));

});

then in the angular component I used below codes.

 import { Observable , fromEvent} from 'rxjs';


fromEvent(window, 'socketEventListen').subscribe((data) =>{
 });

manually download the socket.io client js file and place that in asset folder and use the above codes.