How to send events to client side via node js

Question

I am using client side to send a post request to node js server to perform a long request. During the process, I want the server side can let the client side know how much work is already done and which step it is currently in. So I am wondering if there is a way for the server side to constantly sending events where the client side can receive. Something that can be received by $(document).on(). But It doesn't have to be limited in this way though.

It seems to be $.post only takes data from server side once. So how can I be able to continuously receive server side data after posting?

vitor martins · Accepted Answer · 2020-07-11 19:41:14Z

Since you only want to send messages from the server to the client, you can also use Server-Sent Events (SSE).

You can setup listeners for the SSEs in your client-side script like this:

var serverEvents = new EventSource('http://localhost:8080/events'); serverEvents.addEventListener('message', function(event){ console.log(event.data); });

The browser will send a request to the URL provided when creating the new EventSource to establish a connection, then, from the server, you only need to send the messages in a particular format, for instance:

data: some data data: {"name": "bobby"}

The individual messages must be separated by a pair of newline characters.

Node.js example:

const http = require('http'); const server = http.createServer((req, res) => { if( req.url === '/events'){ res.writeHead(200, { 'Content-Type': 'text/event-stream', 'Cache-Control': 'no-cache', 'Access-Control-Allow-Origin': '*' }); setTimeout(() => { res.write('data: some data\n\n'); }, 1000); } }); server.listen(8080, '127.0.0.1');

Check out this link for more information: https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events

Alongkorn · Accepted Answer · 2016-05-10 14:01:20Z

2

You need to use socket.io to do that.

See this example https://github.com/socketio/socket.io

answered May 10, 2016 at 14:01

Alongkorn

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Comments

andreasonny83 · Accepted Answer · 2016-05-10 13:57:27Z

The only way for creating a real-time communication between server and client side is using websockets. As already mentioned by @Nonemoticoner, the most famous websocket library is Socket.io

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