sse express sample

sse-server.js

import { randomUUID } from "crypto";
import { EventEmitter } from "events";
import express from "express";

function formatEvent(event) {
  const { event = "message", data = {}, id = randomUUID(), retry = undefined } = event;

  const resultString = retry ? `retry: ${retry}\n` : "";
  resultString += `id: ${id}\n`;
  resultString += `event: ${event}\n`;
  resultString += `data: ${JSON.stringify(data)}\n\n`;

  return resultString;
}

const sseEvents = new EventEmitter()

export const sse = (data) => {
  sseEvents.emit("/events", `data: ${JSON.stringify(data)}\n\n`);
}

let counter = 0;
setInterval(() => {
  sse({ payload: {date: Date.now(), times: counter++} });
}, 2000)

export const app = express();

let times = 0;

app.get("/events", (req, res) => {
  res.set({
    "Content-Type": "text/event-stream", // application/x-dom-event-stream
    "Cache-Control": "no-cache, no-transform",
    Connection: "keep-alive",
    "X-Accel-Buffering": "no",
  });
  res.flushHeaders();

  res.write("retry: 10000\n\n");

  sseEvents.on(req.originalUrl.pathname, (data) => {
    res.write(data);
  });
});

app.listen(3000, () => {
  console.log("Listening on port 3000");
});