blog | http2 server push

On the client
you only need to create an EventSource and attach a callback to get data everytime the server pushes

<!doctype html>
<html>

<head>
    <title>Exemple</title>
</head>

<body>
    <p>Open console</p>
</body>
<script>
    var source = new EventSource('/stream');
    source.addEventListener('message', function(event) {
        console.log(event.data);
    }, false);
</script>

</html>

On the server
you need to use the special header "text/event-stream" and write your data prefixed with "data: ".
The client will get data immediately

const express = require('express')
const app = express()

app.get('/', function (req, res) {
    res.sendFile(__dirname+'/index.html');
})

app.get('/stream', function (req, res) {
    res.writeHead(200, {
        'Content-Type': 'text/event-stream',
    });
    var i = setInterval(() => res.write('data: ' + (new Date().toISOString()) +'\n\n'), 1000);
    setTimeout(() => {
        clearInterval(i);
        res.end();
    }, 5000)
})

app.listen(3000, function () {
    console.log('Example app listening on port 3000!')
})

app can also emit and receive event so that streaming a long command can work even if you reload the page.

const express = require('express')
const app = express()

app.get('/', function (req, res) {
    res.sendFile(__dirname+'/index.html');
})

app.get('/eventlisteners', function (req, res) {
    res.send(''+app.rawListeners('event').length);
    console.log(app.rawListeners('event'));
})

app.get('/stream', function (req, res) {
    res.writeHead(200, {
        'Content-Type': 'text/event-stream',
    });
    var handler = (data) => {
        res.write('data: ' + data + '\n\n')
    }
    app.on('event', handler);
    res.on('close', () => {
        app.removeListener('event', handler)
    })
})

app.get('/convert', function (req, res) {
    var i = setInterval(() => 
        app.emit('event', (new Date().toISOString()))
    , 1000);
    setTimeout(() => {
        clearInterval(i);
    }, 5000)
    res.send('ok');
})

app.listen(3000, function () {
    console.log('Example app listening on port 3000!')
})