Data from .json in socket.io - node.js

Question

I have a socket.io connection running with
Client
var socket = io.connect('http://localhost:8080');
socket.on('news', function (data) {
console.log(data);
socket.emit('my other event', { my: 'data' });
});
And server
var app = require('http').createServer(handler)
, io = require('socket.io').listen(app)
, fs = require('fs')
var url = 'pathtojson';
app.listen(8080);
function handler (req, res) {
fs.readFile(__dirname + '/index.html', function (err, data) {
if (err) {
res.writeHead(500);
return res.end('Error loading index.html');
}
res.writeHead(200);
res.end(data);
});
}
io.sockets.on('connection', function (socket) {
socket.emit('news', url);
socket.on('my other event', function (data) {
console.log(data, 'server');
});
});
This is just an example from socket.io. I want to send json data to the client whenever it is updated.
But where do I start ?

Answer 1

You need to have an event fire whenever the data you're interested in updating has changed, and then you need to have the client listen for that event and respond as desired.
You don't really give a context other than "send json data to the client whenever it is updated", so assuming that you are in whatever process is updating your JSON on the server:
if (req.url === '/endpoint') {
yourJSON.foo = 'bar';
// doing whatever you're interested in to the JSON
socket.emit('JSON changed', yourJSON);
//an event is defined by the first argument,
//a value is passed with it as the second
}
NB: Getting more fancy/thoughtful with this means changing your JSON in such a manner that the socket only emits in response to the data change (event, callback, etc). Explicating this pattern is perhaps outside the scope of the question.
Then on the client, you want to define a function to handle those changes:
socket.on('JSON changed', updateFunction);
//where updateFunction is a function you define
//that is expecting arguments that match the output
//from the connected socket.emit event
function updateFunction(newJSON) {
//do whatever with new JSON data
}
This is assuming there is some external endpoint being accessed to update JSON; having it come from a client over socket.io would simply involve defining another event, but this time having it emit from the client, and be listened to by the server.