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This is the source code for - a neat multiplayer online memory/concentration game.

To start the app:

  • Install dependencies with mix deps.get
  • Install Node.js dependencies with npm install
  • Install Elm with npm install -g elm or follow instructions here
  • With Redis installed, start it with redis-server
  • Start Phoenix endpoint with mix phoenix.server

Now you can visit localhost:4000 from your browser.

Below is a brief high-level overview of how things are put together.

Multiplayer features

1 to 4 players may simultaneously take part in the game. The first user always creates the game, then sends out the link to the opponents. The first n-1 users to visit the link become the players, the rest will be able to join the game in the "watch-only" mode.

Game state updates

On the client, the dynamic game state is handled by the Types.Game type (web/static/elm/Types/Game.elm). It includes the state of the board, the current turn, the players' names etc. On every change of this data, the complete state gets broadcast to all other players in JSON format. To minimize the payload, it gets compressed with lz-string, then encoded with base64. Compression/decompression and base64 encoding on the client gets executed via Elm ports.

State persistence

On the server, the game state gets stored in Redis, each game identified with the game:<gameid> key, where gameid is a random string that gets generated at game creation and becomes the last part of the game's URL. The game gets removed from Redis after 24 hours of inactivity.

Why Redis and not an Elixir process? I wanted to make sure ongoing games do not lose their state during deployment.

Known issues

This game won't work in IE, as well as on the networks where websocket traffic is blocked.


There are no tests yet.

Translating game into other languages

If you enjoy this game and want to help translate it into your language, please, submit a PR with the following modifications (based on an example of French):

The very first time

  • Create a new gettext locale with mix gettext.merge priv/gettext --locale=fr

  • Modify /priv/gettext/fr/LC_MESSAGES/default.po

  • Add web/static/elm/I18n/Fr.elm (see web/static/elm/I18n/En.elm for reference)

  • Update web/static/elm/I18n.elm (import the new module and extend the case statement)

  • Copy web/templates/page/index.en.html.eex to web/templates/page/ and translate it

  • Add fr to the list of available locales in config/config.exs and create a new label with Français in web/views/layout_view.ex

Next translation iterations

  • Update /priv/gettext/fr/LC_MESSAGES/default.po

  • Update web/static/elm/I18n/Fr.elm

  • As the web/templates/page/index.en.html.eex reference page may have changed significantly, you may have to copy it to web/templates/page/ again and translate it. It is recommended to keep your previous translated file aside in order to reuse some previous locales in the new translated HTML file

In any cases

If possible, fire up the app and make sure everything compiles and works before submitting the PR.

Copyright (c) 2017 Good Bit Labs Limited, released under MIT