I’m having trouble implementing a general lobby channel in my Phoenix app. Overall, Phoenix makes soft real-time communication very simple. A brief reading off Channels provides all the info to get up and running. However, after reaching that point of joining the channel and broadcasting messages it leaves me with some unanswered questions.

Besides the endpoint, are essentially 3 files in play:

1. socket.js

2. player_socket.ex

3. lobby_channel.ex

I wanted to try the scaffolding so I used the generator mix phx.gen.channel Lobby. This seems to have left me with a “lobby:lobby” topic and subtopic. I tried implementing the presence module several times without any success. How do I implement the presence module so that I can show a list of “online users” and also have a username next to the chat message and the time the message was sent in a readable format, opposed to the Date.new() iso format that the guide provides.

I do have a “current_player” object stored in the session so it should be easy to figure this out but for some reason each time I take one step forward I wind up taking two steps back. I’ve reviewed the docs as well as several tutorials but I can’t figure out what I’m doing wrong.

The whole repo is here.

My player socket:

def connect(%{"token" => token}, socket) do

  case Phoenix.Token.verify(socket, "player socket", token, max_age: @max_age) do
    {:ok, player_id} ->
      {:ok, assign(socket, :player, player_id)}
    {:error, reason} ->
      :error
  end
end

Lobby Channel:

  def join("lobby:lobby", _payload, socket) do
      current_player = socket.assigns.current_player
      players = ChannelMonitor.player_joined("lobby:lobby", current_player)["lobby:lobby"]
      send self, {:after_join, players}
      {:ok, socket}
    end

My Socket.js (which is a mess of failed attempts)

/*jshint esversion: 6 */

// To use Phoenix channels, the first step is to import Socket
// and connect at the socket path in "lib/web/endpoint.ex":
import { Socket } from "phoenix";

var token = $('meta[name=channel_token]').attr('content');
var socket = new Socket('/socket', {params: {token: token}});
socket.connect();

var lobby = socket.channel('lobby:lobby');
lobby.on('lobby_update', function(response) {
  console.log(JSON.stringify(response.players));
});
lobby.join().receive('ok', function() {
  console.log('Connected to lobby!');
});

lobby.on('game_invite', function(response) {
  console.log('You were invited to join a game by', response.username);
});

window.invitePlayer = function(username) {
  lobby.push('game_invite', {username: username});
};



// format timestamp
let formatTimestamp = timestamp => {
    let date = new Date(timestamp);
    return date.toLocaleTimeString();
};

let channel = socket.channel("lobby:lobby", {});
let chatInput = document.querySelector("#chat-input");
let messagesContainer = document.querySelector("#messages");

// listen for "enter" key press
chatInput.addEventListener("keypress", event => {
    if (event.keyCode === 13) {
        channel.push("new_msg", { body: chatInput.value });
        chatInput.value = "";
    }
});

// listen for messages and append to the messagesContainer
channel.on("new_msg", payload => {
    let messageItem = document.createElement("li");
    messageItem.innerText = `[${Date()}] ${payload.body}`;
    messagesContainer.appendChild(messageItem);
});

channel
    .join()
    .receive("ok", resp => {
        console.log("Joined successfully", resp);
    })
    .receive("error", resp => {
        console.log("Unable to join", resp);
    });

export default socket;

// WORKING WITH PHOENIX PRESENCE MODULE //
// channel.on("presence_state", state => {
//     presences = Presence.syncState(presences, state);
//     renderOnlinePlayers(presences);
// });
//
// channel.on("presence_diff", diff => {
//     presences = Presence.syncDiff(presences, diff);
//     renderOnlinePlayers(presences);
// });
// WORKING WITH PHOENIX PRESENCE MODULE //