Simple Way to Implement Server Sent Events in Node.js?
If you're using express this is the easiest way https://www.npmjs.com/package/express-sse
on BE:
const SSE = require('express-sse');
const sse = new SSE();
...
app.get('/sse', sse.init);
...
sse.send('message', 'event-name');
on FE:
const EventSource = require('eventsource');
const es = new EventSource('http://localhost:3000/sse');
es.addEventListener('event-name', function (message) {
console.log('message:', message)
});
Here is an express server that sends one Server-Sent Event (SSE) per second, counting down from 10 to 0:
const express = require('express')
const app = express()
app.use(express.static('public'))
app.get('/countdown', function(req, res) {
res.writeHead(200, {
'Content-Type': 'text/event-stream',
'Cache-Control': 'no-cache',
'Connection': 'keep-alive'
})
countdown(res, 10)
})
function countdown(res, count) {
res.write("data: " + count + "\n\n")
if (count)
setTimeout(() => countdown(res, count-1), 1000)
else
res.end()
}
app.listen(3000, () => console.log('SSE app listening on port 3000!'))
Put the above code into a file (index.js) and run it: node index
Next, put the following HTML into a file (public/index.html):
<html>
<head>
<script>
if (!!window.EventSource) {
var source = new EventSource('/countdown')
source.addEventListener('message', function(e) {
document.getElementById('data').innerHTML = e.data
}, false)
source.addEventListener('open', function(e) {
document.getElementById('state').innerHTML = "Connected"
}, false)
source.addEventListener('error', function(e) {
const id_state = document.getElementById('state')
if (e.eventPhase == EventSource.CLOSED)
source.close()
if (e.target.readyState == EventSource.CLOSED) {
id_state.innerHTML = "Disconnected"
}
else if (e.target.readyState == EventSource.CONNECTING) {
id_state.innerHTML = "Connecting..."
}
}, false)
} else {
console.log("Your browser doesn't support SSE")
}
</script>
</head>
<body>
<h1>SSE: <span id="state"></span></h1>
<h3>Data: <span id="data"></span></h3>
</body>
</html>
In your browser, open localhost:3000
and watch the SSE countdown.
I found SSE implementation in node.js.
Github link: https://github.com/einaros/sse.js
NPM module:https://www.npmjs.com/package/sse
Will above link helps you ?
I'm adding a simple implementation of SSE here. It's just one Node.js file.
You can have a look at the result here: https://glossy-ox.glitch.me/
const http = require('http');
const port = process.env.PORT || 3000;
const server = http.createServer((req, res) => {
// Server-sent events endpoint
if (req.url === '/events') {
res.writeHead(200, {
'Content-Type': 'text/event-stream',
'Cache-Control': 'no-cache',
...(req.httpVersionMajor === 1 && { 'Connection': 'keep-alive' })
});
const refreshRate = 1000; // in milliseconds
return setInterval(() => {
const id = Date.now();
const data = `Hello World ${id}`;
const message =
`retry: ${refreshRate}\nid:${id}\ndata: ${data}\n\n`;
res.write(message);
}, refreshRate);
}
// Client side
res.writeHead(200, {'Content-Type': 'text/html'});
res.end(`
<!DOCTYPE html>
<html lang="en" dir="ltr">
<head>
<meta charset="utf-8">
<title>SSE</title>
</head>
<body>
<pre id="log"></pre>
</body>
<script>
var eventSource = new EventSource('/events');
eventSource.onmessage = function(event) {
document.getElementById('log').innerHTML += event.data + '<br>';
};
</script>
</html>
`);
});
server.listen(port);
server.on('error', (err) => {
console.log(err);
process.exit(1);
});
server.on('listening', () => {
console.log(`Listening on port ${port}`);
});