server.js

import express from 'express';
 import bodyParser from 'body-parser';
 const app = express();
 const port = 3000;
 
 let messages = [];
 
 const sleep = (delay) => new Promise((resolve) => setTimeout(resolve, delay));

 
 app.use(bodyParser.json());
 
 app.use((req, res, next) => {
     res.set('Access-Control-Allow-Origin', '*');
     res.set('Access-Control-Allow-Headers', 'Content-Type');
     next();
 });
 
 app.get('/messages', (req, res) => {
  let filteredMessages = messages.filter(msg => msg.date > new Date(req.query.date ?? null));
  res.json(filteredMessages);
 });
 
 app.get('/messages/longpoll', async (req, res) => {
  let filteredMessages = [];
  do {
      await sleep(1000);
      filteredMessages = messages.filter(msg => msg.date > new Date(req.query.date ?? null));
  } while(filteredMessages.length === 0)
  
  res.json(filteredMessages);
});

app.get('/messages/sse', async (req, res) => {
  res.set('Content-Type', 'text/event-stream');
  res.set('Cache-Control', 'no-cache');
  res.set('Connection', 'keep-alive');
  let closed = false;
  req.on('close', () => {
      closed = true;
  });
  let date = new Date();
  let filteredMessages = [];
  do {
      await sleep(1000);
      filteredMessages = messages.filter(msg => msg.date > date);
      if(filteredMessages.length) {
          let lastMessage = filteredMessages[filteredMessages.length-1];
          date = new Date(lastMessage.date);
      }
      res.write(`event: newmessage\n`);
      res.write(`data: ${JSON.stringify(filteredMessages)}\n\n`);
  } while(!closed)

  res.end();
  //res.json(filteredMessages);
});

 
 app.post('/messages', (req, res) => {
  messages.push({ message: req.body.message, date: new Date()});
     res.json(req.body);
 });
   
 
 
 app.listen(port, () => {
   console.log(`Example app listening on port http://localhost:${port}`);
 });