Tutorial. 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 npm install -g yo
$ sudo npm 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!

Derby game create new game page

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.

Derby multiplayer game tutorial. New game creation

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 = ->
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.

Tutorial on Derby multiplayer game. Name of player

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}}

Tutorial Derby.js multiplayer online game

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 games collection.

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}}

Tutorial derby.js multiplayer game. List of players

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, prof field (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!

Tutorial derby.js multiplayer game. Professor controls

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 = ->
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}}