basic socket service for angular 6 and 7

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';

import { SocketService } from './_services';

@NgModule({
  declarations: [],
  imports: [
    BrowserModule,
  ],
  entryComponents: [],
  providers: [
    SocketService,
  ],
  exports: [
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

socket.service.ts

import { Injectable } from '@angular/core';
import { Subject, Observable } from '../../../node_modules/rxjs';
import * as io from 'socket.io-client';

@Injectable({ providedIn: 'root' })
export class SocketService {

  private url: String = '';
  private socket;

  private socketSubject = new Subject();

  constructor() {
    this.socket = io( this.url );
  }

  public sendMessage( message ) {
    this.socket.emit( 'new-message', message );
  }

  public getMessages = () => {
    return Observable.create( observer => {
      this.socket.on('channelUpdate', message => {
        observer.next( message );
      });
    });
  }

  /**
   * return observable
   */
  listenForAuthenticationChanges(): Observable<any> {
    return this.socketSubject.asObservable();
  }

  /**
   * check for query string and return a better url if present
   *
   * @param url router url
   */
  private getReturnUrl( url: string ) {
    return '';
  }
}