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The result can be found at: https://emojisocket.herokuapp.com/
By clicking on the emojis in the form fieldset you send an event to an underlying websocket server that itself will broadcast the emoji to all connected clients, thus
tl;dr: If you are on the site at the same time with multiple people (or in multiple tabs, windows) you can send each other emojis. :)
Unfortunately the workflow of Heroku warming up and killing applications quite fast (at least in my free plan), the client connection time is only about a few minutes and afterwards you get unconnected from the server again, thus clicking afterwards on the emojis will not effect anything.