npm install express socket.io socket.io-client

"express": "^4.17.1",
"socket.io": "^3.0.4",
"socket.io-client": "^3.0.4",

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

const io = require('socket.io')(http, {
 cors: {  // 处理跨域问题
  origin: "http://localhost:4300", // angular项目的启动端口，默认4200，本人项目的启动端口为4300，大家根据自己情况修改
  methods: ["GET", "POST"],
  credentials: true
 }
});

io.on('connection', (socket) => {
 console.log('user connected');

 socket.on('add-message', (message) => {
  io.emit('message', {type: 'new-message', text: message});
 });
})

http.listen(4000, () => { // 后台服务启动端口
 console.log('start on 4000....');
})

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

@Injectable()
export class ChatService {
 private url = 'http://localhost:4000'; // 后台服务端口
 private socket: any;

 sendMessage(message: any) {
  this.socket.emit('add-message', message);
 }

 getMessages(): Observable<any> {
  return new Observable(observer => {
   this.socket = io(this.url, {withCredentials: true});
   this.socket.on('message', (data) => {
    observer.next(data);
   });
   return () => {
    this.socket.disconnect();
   }
  })
 }
}

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

@Component({
 selector: 'test-chat',
 template: `<div *ngFor="let message of messages">
        {{message.text}}
       </div>
       <input [(ngModel)]="message" />
       <button (click)="sendMessage()">Send</button>`,
 providers: [ChatService] // 注入依赖
})
export class TestChatComponent implements OnInit, OnDestroy {
 messages = [];
 connection: any;
 message: any;

 constructor(private chatService: ChatService) {
 }

 sendMessage() {
  this.chatService.sendMessage(this.message);
  this.message = '';
 }

 ngOnInit() {
  this.connection = this.chatService.getMessages()
   .subscribe(message => {  // 组件初始化时订阅信息
    this.messages.push(message);
   });
 }

 ngOnDestroy() {
  this.connection.unsubscribe();  // 组件销毁取消订阅
 }
}

import { io } from 'socket.io-client';