Data output in real time to the browser without restarting node js, websocket?

Question

I need to get currency quotes in real time, without reloading the page and clicking on buttons.

To solve this problem, we had to resort to the following technologies: node js, websocket.io, Redis, data donor API.

In the console I get the following data:

{"symbol": "EURUSD", "bid": 1.13624, "ask": 1.13624, "price": 1.13624}

in fact, everything works, and this is what I need. But, I can not figure out how to transfer the same data to the browser, so that it would be like this:

EURUSD | bid - 1.13624 | ask - 1.13624 | price - 1.13624

Here is the js code:

const redis = require('redis');
const settings = {
    REDIS: {
        HOST: 'localhost'
    }
}
let redisClient = new redis.createClient(settings.REDIS);

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

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

http.listen(3000, function(){
  console.log('listening on *:3000');
});

function getQuote(symbol, callback) {
    redisClient.get(symbol, (error, quote) => {
        if (error) {
            throw new Error(error);
        }
        quote = JSON.parse(quote);
        callback(quote);
    });
}

setInterval(() => {
    getQuote('EURUSD', (q) => {
        const formattedQ = `${q.SYMBOL} | bid - ${q.bid} | ask - ${q.ask} | price - ${q.price}`;
        console.log(formattedQ);
    });
}, 10);

io.on('connection', function(socket){
    socket.on('get_quote', function(msg){
        io.emit('get_quote', getQuote('EURUSD', (q) => /* ??? what to insert here? -> (formattedQ) ??? */));
    });
});

And HTML file:

<script src="/socket.io/socket.io.js"></script>
<script src="https://code.jquery.com/jquery-1.11.1.js"></script>
<script>
  $(function () {
    var socket = io();
    socket.on('get_quote', function(msg){
      // ??? what to insert here to update quotes without rebooting ???
    });
  });
</script>

Answer 1

I think a more suitable approach would be to send the json as-is, and format it in the client.

/* redis connection code */
setInterval(() => {
    getQuote('EURUSD', (q) => {
        const formattedQ = `${q.SYMBOL} | bid - ${q.bid} | ask - ${q.ask} | price - ${q.price}`;
        console.log(formattedQ);
    });
}, 10);

Update

I'm revising the answer because I think it would be easier to show a piece of code I believe would work. In order to send data from the server to the client, you should use the io.emit() function, which you do - but you wrapped it in a socket.on('get_quote') . Basically what will happen is that you will emit a new message only if a message was received (resulting in a deadlock).

I believe this snippet should work:

io.on('connection', function(socket){
    setInterval(() => {
        getQuote('EURUSD', (q) => {
            io.emit('get_quote', q);
        });
    }, 10);
});

This would initialize an interval when there is a connection to the server, and emit a new q every 10 seconds.
Then, in your HTML file you should receive the q (in JSON form), and format it the way you choose:

socket.on('get_quote', function(msg){
    console.log(`${msg.SYMBOL} | bid - ${msg.bid} | ask - ${msg.ask} | price - ${msg.price}`);
});