Multiplayer game on Derby.js

In this tutorial we're going to create a simple online multiplayer game on Derby.js

The game

The professor creates a question: “Guess the number of jelly beans in the jar.” Everyone has to enter. Once the professor closes the game, the average is displayed to everyone. No more people can enter the game. People can enter the game without a login.

Generating project

Create a project using generator-derby:

$ sudo install -g yo
$ sudo install -g generator-derby
$ mkdir my-app
$ cd my-app
$ yo derby --coffee
$ npm start

Creating game

We want to create a game which has a name and a question in it. Create two inputs and a ‘Create new game!’ button, wrapped in a form which has a ‘post’ method.

home.jade

form(method='post', action='/create_game')
  p Type the name of the game:
  input(type='text', name='name')
  p Type the question:
  input(type='text', name='question')
  br
  br
  button Create new game!

Write a controller that handles /create_game action.

index.coffee

app.post '/create_game', (page, model, params) ->
  model.add 'games', {
    name: params.body.name
    question: params.body.question
    players: {}
    userIds: []
  }, ->
    page.redirect '/'

Here we create a game: add a new games document with a name, a question, an empty object with players and an array with userIds (we need them to easily loop through all players in the game). model.add also generates an id for each game. As for form variables (name, question), we get them from params.body in the controller. We redirect to / page, because we want to stay on the same page after creating the game. Let’s display the games on the home page. Each game will be a link.

List of games

To be able to loop through the games in games collection (in order to display the list of games) we need to create a local db out of games, convert it to an array and make a reference in private _page collection.

index.coffee

app.get '/', (page, model) ->
  model.subscribe 'games', ->
    model.at('games').filter().ref '_page.games'
    page.render 'home'

We are subscribing for games collection to make it accessible on / page. model.at creates a local games db,filter() converts games to an array and ref() creates a reference from this array. Now we can loop through the array of games in views:

home.jade

p Games:
each #root._page.games as #game
  a(href='/game/{{#game.id}}') {{#game.name}}

We are displaying each game as a link which will redirect us to the game page. id and name are the fields in game object. Let’s add a game.

Deleting games

To delete all the games add a ‘Delete all games!’ input.

home.jade

input(on-click='deleteGames()', type='submit', 
      value='Delete all games!') 

When clicking it, deleteGames function is triggered.

index.coffee

app.proto.deleteGames = ->
  @model.subscribe 'games', =>
    games = @model.get 'games'
    for key of games
      @model.del "games.#{key}"

We need to loop through games deleting each game from games collection. It is necessary to subscribe for games and set it into a variable. for of loop goes through each game and model.del deletes each game. Notice that in the last line we used double quotes. String in double quotes supports interpolation. In this case, we interpolate key, that is game id.

Adding player’s name

Let’s add player’s name.

home.jade

p Player's name:
form(on-submit='setUserName()')
  input(type='text', value='{{#root._page.userName}}'')
  br
  br
  button(type=’submit’) Save!

We are binding the value of the input. Submitting the form triggers setUserName function.

index.coffee

app.proto.setUserName = ->
  userId = this.model.get '_session.userId'
  userName = this.model.get '_page.userName'
  if userName?
    userName = userName.trim()
  if userName
    this.model.set 'users.' + userId + '.userName', userName
    this.model.del '_page.userName'
  else
    alert 'Name cannot be empty!'

We get userName from _page.userName, trim and set it to users collection. If an empty input is submitted we show "Name cannot be empty!" alert message Also, let’s greet the player. To do this, we subscribe for current user (not for players, because name is stored in users collection). We also need to get userId, which is stored in private collection_session.userId and set it in a variable to be able to subscribe for current user.

index.coffee

app.get '/', (page, model) ->
   userId = model.get ‘_session.userId’
   model.subscribe 'games', ‘users.’ + userId,  ->
     model.ref ‘_page.user’, ‘users.’ + userId
     model.at('games').filter().ref '_page.games'
     page.render 'home'

There is a reference (model.ref) on the current user and now we can check in views if the user has name. If he does, the greeting appears on the page.

p Player's name:
form(on-submit='setUserName()')
  input(type='text', value='{{#root._page.userName}}'')
  br
  br
  button(type=’submit’) Save!
  if #root._page.user.userName
    p Hello, {{#root.users[#root._session.userId].userName}}

Game page

Add game.jade file to /views/app and import it to index.jade

game.jade

index: 

index.jade

import:(src='./home')
import:(src='./game')

Title:
  | {{_page.title}}

Body:
  view(name='header')
  view(name='{{$render.ns}}')
  view(name='footer', year='2014')

header:
  h1 Header

footer:
  p Footer {{@year}}

Create a controller that handles game page.

index.coffee

app.get '/game/:gameId', (page, model, params) ->
  page.render ‘game’

Display the question

We want to display the question in the game. To do that, subscribe for the game (and make a reference for easy access), set the game id and make a reference, so that we can access the game id in views.

app.get '/game/:gameId', (page, model, params) ->
  model.subscribe ‘games.’ + params.gameId, ->
    model.set ‘_page.gameId’, params.gameId 
    page.render ‘game’

Here comes the views.

game.jade

index:  
|+  p {{#root.games[#root._page.gameId].question}}

Add input for the answer

game.jade

index:  
  p {{#root.games[#root._page.gameId].question}}
|+  form(on-submit='setAnswer()')
|+    input(type='text', value='{{#root._page.answer}}')
|+    br
|+    button Save

Let’s subscribe for the users in the game (because we want to display players in the game) and make references to players, current user, current game and current player. To subscribe for users in the game, we need to make a query request.

app.get '/game/:gameId', (page, model, params) ->
  model.subscribe ‘games.’ + params.gameId, ->
    model.set ‘_page.gameId’, params.gameId 
|+    usersInGame = model.query 'users', 'games.' + params.gameId + 
|+                  '.userIds'
|+    userId = model.get '_session.userId'
|+    model.subscribe usersInGame, 'users.' + userId, ->
|+      model.set '_page.gameId', params.gameId
|+      model.ref '_page.user', 'users.' + userId
|+      model.ref '_page.game', 'games.' + params.gameId
|+      model.ref '_page.players', 'games.' + params.gameId + '.players'
|+      model.ref '_page.player', 'games.' + params.gameId +
|+                '.players.' + userId
      page.render 'game'

Add player to the game

index.coffee

app.get '/game/:gameId', (page, model, params) ->
  model.subscribe ‘games.’ + params.gameId, ->
    model.set '_page.gameId', params.gameId 
    usersInGame = model.query 'users', 'games.' + params.gameId + 
                  '.userIds'
    userId = model.get '_session.userId'
    model.subscribe usersInGame, 'users.' + userId, ->
      model.set '_page.gameId', params.gameId
      model.ref '_page.user', 'users.' + userId
      model.ref '_page.game', 'games.' + params.gameId
      model.ref '_page.players', 'games.' + params.gameId + '.players'
      model.ref '_page.player', 'games.' + params.gameId + 
                '.players.' + userId
|+      unless model.get '_page.player'
|+        model.add '_page.players', { id: userId }
|+        model.push '_page.game.userIds', userId   
      page.render 'game'

When opening the game page, the player is added to the game, unless he is already there. model.add adds a new document with random id. It is possible to specify an id. We want players’ ids to be the same as users’ ids, that is why we set id as userId. When the player is added, his id is saved into game’s userIds array.

Save the answer

index.coffee

app.proto.setAnswer = ->
  answer = this.model.get '_page.answer'
  unless answer?
    answer = ""
  answer = parseInt( answer.trim() )
  if isNaN( answer )
    alert 'The answer must be a number!'
  else
    this.model.set '_page.player.answer', answer
    this.model.del '_page.answer'

We are get the answer from _page.answer and set it to answer, checking whether it is not undefined or null and parsing it to integer. If the answer is NaN, we alert "The answer must be a number!". Otherwise the answer is set to gamescollection.

Since we’ve made a reference, we don’t need to write the full path ('games.' + params.gameId + '.players.' + userId) — we are setting the answer to _page.player.answer. We also want to display the answer on the game page. When the player changes his mind and enters a different guess, the answer on the page will be changed instantly. The answer should be displayed only if there is one, so we make an if-statement checking if there is an answer.

game.jade

  if #root._page.player.answer
    p Your answer is {{#root._page.player.answer}}

List of players in the game

Let’s display all players in the game.

game.jade

  p Players in the game
  each #root._page.game.userIds as #userId
    p {{#root.users[#userId].userName}}

Giving control to prof

Only the professor should be able to create a game, not the students. Add an input (type checkbox). If it is checked, proffield (this field is created in _page.user when the checkbox is checked) becomes true. Only when it is true the game can be created.

home.jade

index:
  label
    input(type='checkbox', checked='{{#root._page.user.prof}}')
    |  Professor
  if #root._page.user.prof
    form(method='post', action='/create_game')
      p Type the name of the game:
      input(type='text', name='name')
      p Type the question:
      input(type='text', name='question')
      br
      br
      button Create new game!

Besides, only the professor should be able to finish the game. We have already subscribed for the current user and made a reference (_page.user).

Write an if-statement which will check if the user is the professor. If he is, then the "Finish the game!" button will be displayed.

game.jade

  if #root._page.user.prof
    input(on-click='finishGame()', type='submit', 
          value='Finish the game!')

Finish the game

Now let’s write the controller that handles finishing the game. The aim here is to collect the answers, strike an average and finish the game. To collect the answers, use the for of loop. The controller sets _page.game.finish to true.

index.coffee

app.proto.finishGame = ->
  players = this.model.get '_page.players'
  average = 0
  for key, value of players
    average += value.answer
  numberOfPlayers = this.model.get('_page.game.userIds').length
  average = average / numberOfPlayers
  this.model.set '_page.game.average', average
  this.model.set '_page.game.finish', true

No going back

When the game is finished by professor, we want all the players inside the game to automatically go to the results page. To do that, we need to create a component from the view we render. For convenience, the name of the component should match the name of the template it’s associated with.

We use component’s create method to execute code right after this component (in our case it’s the whole page) has been rendered. When the professor clicks "Finish the game!", _page.game.finish becomes true. So we want to listen for_page.game.finish variable changes. And if the game is finished, we want players to be redirected to the page with the results.

index.coffee

app.component 'game', class Game
  create: ->
    gameId = this.model.root.get '_page.gameId'
    this.model.root.on 'change', '_page.game.finish', (value) ->
      app.history.replace '/game/' + gameId + '/results'

New players shouldn’t be able to enter the game if it has been finished, so when going to the game page, we are checking whether the game is finished or not.

Results

index.coffee

app.get '/game/:gameId', (page, model, params) ->
|+  model.subscribe 'games.' + params.gameId, ->
|+    if model.get 'games.' + params.gameId + '.finish'
|+      page.redirect '/game/' + params.gameId + '/results'
|+      return

Add results.jade file to /views/app and import it to index.jade:

result.jade

index:

index.jade

import:(src='./results')

Here is the controller that handles results page.

index.coffee

app.get '/game/:gameId/results', (page, model, params) ->
  model.subscribe 'games.' + params.gameId, ->
    model.ref '_page.average', 'games.' + params.gameId + '.average'
    page.render 'results'

We subscribe for the game and make a reference to the average, which is stored in games collection. And, finally, display the results on the results page.

results.jade

index:
  p The average is {{#root._page.average}}

Final code

index.coffee

derby = require 'derby'

app = module.exports = derby.createApp 'app', __filename

global.app = app unless derby.util.isProduction

app.serverUse module, 'derby-jade'
app.serverUse module, 'derby-stylus'

app.loadViews __dirname + '/../../views/app'
app.loadStyles __dirname + '/../../styles/app'

app.get '/', (page, model) ->
  userId = model.get '_session.userId'
  model.subscribe 'games', 'users.' + userId, ->
    model.ref '_page.user', 'users.' + userId
    model.at('games').filter().ref '_page.games'
    page.render 'home'

app.post '/create_game', (page, model, params) ->
  model.add 'games', {
    name: params.body.name
    question: params.body.question
    players: {}
    # to have access to all players in the game
    userIds: []
  }, ->
    page.redirect '/'

app.get '/game/:gameId', (page, model, params) ->
  model.subscribe 'games.' + params.gameId, ->
    if model.get 'games.' + params.gameId + '.finish'
      page.redirect '/game/' + params.gameId + '/results'
      return
    model.set '_page.gameId', params.gameId
    usersInGame = model.query 'users', 'games.' + params.gameId + 
                  '.userIds'
    userId = model.get '_session.userId'
    model.subscribe usersInGame, 'users.' + userId, ->
      userId = model.get '_session.userId'
      model.set '_page.gameId', params.gameId
      model.ref '_page.user', 'users.' + userId
      model.ref '_page.game', 'games.' + params.gameId
      model.ref '_page.players', 'games.' + params.gameId + '.players'
      model.ref '_page.player', 'games.' + params.gameId +
                '.players.' + userId
      unless model.get '_page.player'
        model.add '_page.players', { id: userId }
        model.push '_page.game.userIds', userId

      page.render 'game'

app.get '/game/:gameId/results', (page, model, params) ->
  model.subscribe 'games.' + params.gameId, ->
    model.ref '_page.average', 'games.' + params.gameId + '.average'
    page.render 'results'

app.proto.deleteGames = ->
  @model.subscribe 'games', =>
    games = @model.get 'games'
    for key of games
      @model.del "games.#{key}"

app.proto.setUserName = ->
  userId = this.model.get '_session.userId'
  userName = this.model.get '_page.userName'
  if userName?
    userName = userName.trim()
  if userName
    this.model.set 'users.' + userId + '.userName', userName
    this.model.del '_page.userName'
  else
    alert 'Name cannot be empty!'

app.proto.setAnswer = ->
  answer = this.model.get '_page.answer'
  unless answer?
    answer = ""
  console.log answer
  answer = parseInt( answer.trim() )
  if isNaN( answer )
    alert 'The answer must be a number!'
  else
    this.model.set '_page.player.answer', answer
    this.model.del '_page.answer'

app.proto.finishGame = ->
  players = this.model.get '_page.players'
  average = 0
  for key, value of players
    average += value.answer
  numberOfPlayers = this.model.get('_page.game.userIds').length
  average = average / numberOfPlayers
  this.model.set '_page.game.average', average
  this.model.set '_page.game.finish', true

app.component 'game', class Game
  create: ->
    gameId = this.model.root.get '_page.gameId'
    this.model.root.on 'change', '_page.game.finish', (value) ->
      app.history.replace '/game/' + gameId + '/results'

home.jade

index:
  label
    input(type='checkbox', checked='{{#root._page.user.prof}}')
    |  Professor
    if #root._page.user.prof
      form(method='post', action='/create_game')
        p Type the name of the game:
        input(type='text', name='name')
        p Type the question:
        input(type='text', name='question')
        br
        br
        button Create new game!

  p Player's name:
  form(on-submit='setUserName()')
    input(type='text', value='{{#root._page.userName}}', name='name')
    br
    br
    input(type='submit', value='Save!')
    if #root._page.user.userName
      p Hello, {{#root.users[#root._session.userId].userName}}

  p Games:
  each #root._page.games as #game
    a(href='/game/{{#game.id}}') {{#game.name}}
    br
  br

  input(on-click='deleteGames()', type='submit', 
        value='Delete all games!')

game.jade

index:
  p Game
  p {{#root.games[#root._page.gameId].question}}
  form(on-submit='setAnswer()')
    input(type='text', value='{{#root._page.answer}}')
    br
    button Save
  br
  if #root._page.player.answer
    p Your answer is {{#root._page.player.answer}}

  p Players in the game
  each #root._page.game.userIds as #userId
    p {{#root.users[#userId].userName}}

  if #root._page.user.prof
    input(on-click='finishGame()', type='submit', 
          value='Finish the game!')

results.jade

index:
  p The average is {{#root._page.average}}