SSE: 'onmessage' never gets called
Question
I'm following the most simple tutorials on the internet about how to listen to Server-Sent Events from Javascript:
var es = new EventSource('url')
es.onmessage = function (e) { console.log(e.data) }
But my message handlers never get called. onopen and onerror handlers do get called, Chrome Developer Tools do show a nice "stream" view of the events being sent by the server and if I do the same call from curl I get a stream of events nicely formatted in the correct way. What could be wrong?
2 answers
solution1
2 ACCPTED 2019-08-26 01:08:59
Just realized, from this tutorial , that you can associate an event name with each server-sent event.
When you do that, the message listener stops getting called and instead you have to setup a new special listener for each kind of event you're sending. I was doing that on my server.
So instead of es.onmessage = function () {...} I had to do es.addEventListener("special-event-name", function () {...}) .
solution2
0 2019-12-17 22:35:28
Here is a minimal example showing how you can get the default message event type and a custom event type on the same SSE stream.
<html lang="en">
<body>
<div id="payload"></div>
<script>
const stream = new EventSource('https://url-goes-here');
stream.addEventListener('message', (event) => {
document.getElementById('payload').innerText = `Received a regular message: ${event.data}`;
}, false);
stream.addEventListener('myEvent', (event) => {
document.getElementById('payload').innerText = `Received a myEvent message: ${event.data}`;
}, false);
</script>
</body>
</html>
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