sse.js

var http = require('http')

http.createServer(function (req, res) {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive'
  })
  res.write('retry: 10000\n')
  res.write('event: connecttime\n')
  res.write('data: ' + (new Date()) + '\n\n')
  res.write('data: ' + (new Date()) + '\n\n')

  var interval = setInterval(function () {
    res.write('data: ' + (new Date()) + '\n\n')
  }, 1000)

  req.connection.addListener('close', function () {
    clearInterval(interval)
  }, false)
}).listen(8080)

Blatantly stolen from https://github.com/yoshuawuyts/knowledge/blob/master/browser/sse.md