Real-time example in Node.js

app.js

var express = require('express')
  , app = express()
  , sse = require('./sse')

var connections = []
  , votes = {yes: 0, no: 0}

app.engine('jade', require('jade').__express)
app.set('view engine', 'jade')

app.use(sse)

app.get('/', (req, res) => {
  res.render('vote')
})

app.get('/result', (req, res) => {
  res.render('result')
})

app.get('/vote', (req, res) => {
  if (req.query.yes === "true") 
    votes.yes++
  else 
    votes.no++

  for(var i = 0; i < connections.length; i++) {
    connections[i].sseSend(votes)
  }
  res.sendStatus(200)
})

app.get('/stream', (req, res) => {
  res.sseSetup()
  res.sseSend(votes)
  connections.push(res)
})

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

result.jade

doctype html
html
  head
    title Voting results for world peace
  body
    div(id="votes") Yes: 0, No: 0
    div(id="state") Disconnected
  script(src="//code.jquery.com/jquery-2.1.4.min.js")
  script.
    if (!!window.EventSource) {
      var source = new EventSource('/stream')

      source.addEventListener('message', (e) => {
        votes = JSON.parse(e.data)
        $("#votes").text("Yes: " + votes.yes + ", No: " + votes.no)
      }, false)

      source.addEventListener('open', (e) => {
        $("#state").text("Connected")
      }, false)

      source.addEventListener('error', (e) => {
        if (e.target.readyState == EventSource.CLOSED) {
          $("#state").text("Disconnected")
        }
        else if (e.target.readyState == EventSource.CONNECTING) {
          $("#state").text("Connecting...")
        }
      }, false)
    } else {
      console.log("Your browser doesn't support SSE")
    }

sse.js

module.exports = (req, res, next) => {
  res.sseSetup = () => {
    res.writeHead(200, {
      'Content-Type': 'text/event-stream',
      'Cache-Control': 'no-cache',
      'Connection': 'keep-alive'
    })
  }

  res.sseSend = (data) => {
    res.write("data: " + JSON.stringify(data) + "\n\n")
  }
  next()
}

vote.jade

doctype html
html
  head
    title Voting for the world peace
  body
    h1 Will "Hello, World!" bring world peace?
    <div id="yes">Yes</div>
    <div id="no">No</div>
    <div id="message"></div>
  script(src="//code.jquery.com/jquery-2.1.4.min.js")
  script.
    function vote(yes) {
      $.get("/vote?yes=" + yes, () => {
        $("#yes").hide()
        $("#no").hide()
        $("#message").text("Thank you for your vote!")
      })
    }
    
    $("#yes").on("click", () => {
      vote(true)
    })

    $("#no").on("click", () => {
      vote(false)
    })