server.js

const EventEmitter = require("eventemitter3")
const emitter = new EventEmitter()
const express = require("express")
const cors = require("cors")
var app = express()

const subscribe = (req, res) => {
  res.writeHead(200, {
    "Content-Type": "text/event-stream",
    "Cache-Control": "no-cache",
    Connection: "keep-alive"
  })

  const onMessage = data => {
    res.write(`data: ${JSON.stringify(data)}\n\n`)
  }

  emitter.on("message", onMessage)

  req.on("close", function() {
    emitter.removeListener("message", onMessage)
  })
}

const publish = (req, res) => {
  emitter.emit("message", req.body)
  res.json({ message: "success" })
}

app.use(cors())
app.use(express.json())
app.post("/", publish)
app.get("/", subscribe)
app.listen(3000, () => {})