How to connect to Heroku custom domain via socket.io?

Question

JavaScript

There is a design:

//client.js

var io = require('socket.io-client');

var socket = io.connect('https://app.herokuapp.com', {reconnect: true});

// Add a connect listener
socket.on('connect', function (data) {
    console.log('Connected!');
});

But for some reason, when linking a custom domain (the domain is normally linked and the heroku instance is paid), the connection does not occur:

//client.js

var io = require('socket.io-client');

var socket = io.connect('https://app.com', {reconnect: true});

// Add a connect listener
socket.on('connect', function (data) {
    console.log('Connected!');
});

Answer 1

The question is closed, everything worked by itself. Apparently, there was something with DNS.

Answer 2

1. Does https://app.com belong to you?
2. Specify your address in the browser (or curl, wget, etc.) (do not forget about the port) and check for yourself what is wrong.