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HTML

              
                <div class="screen screen--intro">
  <div class="textbox">
    <p>Welcome to my little game of memo! It's build as a object-oriented JavaScript state machine. Images come from FontAwesome.</p>
    <p class="center"><a class="textbox__button introbox__button" href="#screen--table">Play</a></p>
  </div>
</div>
<div class="screen screen--table">
  <div class="l_cards">
  </div>
  <div class="moves">
    0
  </div>
  
  <!-- score counter -->
  <!-- place cards ~pleasingly~ in the middle of the table. "divisible by x"? -->
</div>
<div class="screen screen--end">
  <div class="textbox">
    <p>Hurrah! You won! You finished the game in <strong class="final-move-count"></strong> moves.</p>
    <p class="center"><a class="textbox__button endbox__button" href="#screen--table">Play again</a></p>
  </div>
</div>
              
            
!

CSS

              
                  html,body {
  height:100%;
  margin:0;
}

body {
  font-family:Arial, sans-serif;
  line-height:1.5em;
}

.screen {
  display:none;
  width:100%;
  height:100%;
  min-height:100%;/*for mozilla*/
  
}

.screen--active {
  display:flex;
}

.screen--intro,
.screen--end{
  background-color:#7CB342;
  align-items:center;
  justify-content:center;
}

.textbox {
  background-color:#ffffff;
  width:30em;
  margin:auto;
  padding:1em;
  border-radius:0.2em;
}

.textbox__button {
  display:inline-block;
  text-align:center;
  background-color:#7CB342;
  width:auto;
  padding:0.4em;
  color:#ffffff;
  text-decoration:none;
  border-radius:0.2em;
}
.textbox__button:hover,
.textbox__button:focus {
  color:#004D40;
}

.screen--table {
  align-items:center;
  justify-content:center;
  align-content:center;
}

.l_cards {
  display: flex;
  flex-wrap:wrap;
  align-content:center;
  align-items:left;
  justify-content:left;
  width: 90%;
  max-width: 40em;
  height: 90%;
  margin: 0 auto;
}

.card {
  font-size:100%;
  background-color:#7CB342;
  color:#004D40;
  border-radius:0.2em;
  text-align:center;
  color:white;
  display:flex;
  align-items:center;
  justify-content:center;
}

.card i {
  
}

p.center {
  text-align:center;
}

.moves {
  position:absolute;
  top:0;
  left:0;
  background-color:#7CB342;
  padding:0.5em;
  color:#fff;
}
              
            
!

JS

              
                const cardImages = ['ambulance',
'anchor',
'archive',
'award',
'balance-scale',
'bath',
'bed',
'beer',
'bell',
'bell',
'bicycle',
'binoculars',
'birthday-cake',
'blender',
'bomb',
'book',
'bookmark',
'briefcase',
'broadcast-tower',
'bug',
'building',
'bullhorn',
'bullseye',
'bus',
'calculator',
'calendar',
'calendar-alt',
'camera',
'camera-retro',
'car',
'church',
'clipboard',
'cloud',
'coffee',
'cog',
'cogs',
'compass',
'cookie',
'cookie-bite',
'copy',
'crow',
'cube',
'cubes',
'cut',
'dice',
'dice-five',
'dice-four',
'dice-one',
'dice-six',
'dice-three',
'dice-two',
'digital-tachograph',
'door-closed',
'door-open',
'dove',
'drum',
'drum-steelpan',
'envelope',
'envelope-open',
'eraser',
'eye',
'eye-dropper',
'fax',
'feather',
'feather-alt',
'fighter-jet',
'file',
'file-alt',
'file-prescription',
'film',
'fire',
'fire-extinguisher',
'fish',
'flag',
'flag-checkered',
'flask',
'frog',
'futbol',
'gamepad',
'gavel',
'gem',
'gift',
'glass-martini',
'glasses',
'globe',
'graduation-cap',
'hdd',
'headphones',
'headphones-alt',
'headset',
'heart',
'helicopter',
'highlighter',
'home',
'hospital',
'hourglass',
'image',
'images',
'industry',
'key',
'keyboard',
'kiwi-bird',
'laptop',
'leaf',
'lemon',
'life-ring',
'lightbulb',
'lock',
'lock-open',
'magic',
'magnet',
'map',
'map-marker',
'map-marker-alt',
'map-pin',
'map-signs',
'marker',
'medal',
'medkit',
'memory',
'microchip',
'microphone',
'microphone-alt',
'mobile',
'mobile-alt',
'money-bill',
'money-bill-alt',
'money-check',
'money-check-alt',
'moon',
'motorcycle',
'newspaper',
'paint-brush',
'paper-plane',
'paperclip',
'paste',
'paw',
'pen',
'pen-alt',
'pen-fancy',
'pen-nib',
'pencil-alt',
'phone',
'plane',
'plug',
'print',
'puzzle-piece',
'road',
'rocket',
'ruler-combined',
'ruler-horizontal',
'ruler-vertical',
'save',
'school',
'screwdriver',
'search',
'shield-alt',
'shopping-bag',
'shopping-basket',
'shopping-cart',
'shower',
'snowflake',
'space-shuttle',
'star',
'sticky-note',
'stopwatch',
'subway',
'suitcase',
'sun',
'tablet',
'tablet-alt',
'tachometer-alt',
'tag',
'tags',
'taxi',
'thumbtack',
'ticket-alt',
'toolbox',
'train',
'trash',
'trash-alt',
'tree',
'trophy',
'truck',
'tv',
'umbrella',
'university',
'unlock',
'unlock-alt',
'utensil-spoon',
'utensils',
'wallet',
'weight',
'wheelchair',
'wine-glass',
'wrench'
];

const cardSizing = {
  width:3,
  height:4,
  margin:0.1
}

class Card {
  constructor(symbol,parent,color) {
    this.symbol = symbol;
    this.parent = parent;
    this.color = color;
    this.backColor = '#c0c0cc';
    this.flipped = false;
    this.element = document.createElement('div');
    this.element.style.width= cardSizing.width +"em";
    this.element.style.height = cardSizing.height + "em";
    this.element.style.margin = cardSizing.margin + "em";
    this.element.classList.add("card");    
  }  
  draw() {
    this.parent.appendChild(this.element);
   this.flipBack(); 
  }
  
  flipFront() {
    console.log("image: "+this.symbol);
    this.flipped = true;
    this.element.innerHTML = `<i class="fas fa-${this.symbol}"></i></div>`;
    console.log("color: "+this.color);
    this.element.style.backgroundColor = this.color;
    this.element.removeEventListener('click',this);
  }
  flipBack() {
    this.flipped = false;
    this.element.innerHTML = `<i class="fas fa-stroopwafel"></i></div>`;
    this.element.style.backgroundColor = this.backColor;
    this.element.addEventListener('click',this); //I really like this trick: you can pass an object with a method handleEvent(event) instead of a named/anonymous function. It dramatically simplifies scoping! Cred: https://medium.com/@photokandy/til-you-can-pass-an-object-instead-of-a-function-to-addeventlistener-7838a3c4ec62
  }
  remove() {
    this.element.style.visibility = 'hidden';
  }
  handleEvent(event) {
    if (event.type == 'click') {
      game.increaseCounter();
      game.dispatch('cardClick',this);
    }
  }
}
      //I'm working from this design: https://www.smashingmagazine.com/2018/01/rise-state-machines/
const game = {
  cardCount:10,
  images:cardImages,
  cards:[],
  cardsLeft:0,
  moves:0,
  firstCard:null,
  secondCard:null,
  state:null,
  screen:null,
  increaseCounter() {
    this.moves++;
    this.moveCounter.innerHTML = this.moves;
  },
  resetGameValues() {
    this.cards = [];
    this.cardsLeft = this.cardCount;
    this.moves = 0;
    this.firstCard = null;
    this.secondCard = null;
  },
  dispatch(actionName, ...payload) {
    const actions = this.states[this.state];
    const action = this.states[this.state][actionName];
    
    if (action) {
      action.apply(game, payload);
    }
  },
  changeStateTo(newState) {
    this.state = newState;
  },
  setScreenTo(newScreen) {
    if (this.screen != null) {
      document.getElementsByClassName('screen--'+this.screen)[0].classList.remove('screen--active');
    }    
    document.getElementsByClassName('screen--'+newScreen)[0].classList.add('screen--active');
    this.screen = newScreen;
  },
  states:{
    'init':{
      setup:function() {
        console.log("setting up the game");
        this.setScreenTo('intro');
        this.changeStateTo('intro');
        document.getElementsByClassName('introbox__button')[0].addEventListener('click',function(event) {
          game.dispatch('click');
        });
      }
    },
    'intro':{
      click:function(){
        console.log("transition: dealing");
        this.setScreenTo('table');
        this.resetGameValues();
        let cards = document.getElementsByClassName("l_cards")[0];
        while (cards.firstChild) {
          cards.removeChild(cards.firstChild)
        };
        
        let area = (cardSizing.width+cardSizing.margin)*(cardSizing.height+cardSizing.margin)*this.cardCount*2;
        cards.style.maxWidth = Math.ceil(Math.sqrt(area))+"em";
        
        let symbolsFound = 0;
        let color = [0,80,40];
        let imgLength = this.images.length;
        let randObj = {};
        while (symbolsFound<this.cardCount) {
          let ind = Math.floor(imgLength*Math.random());
          if(randObj[ind]) {
            continue;
          } else {
            randObj[ind] = true;
            symbolsFound++;
          }
        }        
        let symbolIndexes = Object.keys(randObj);
        for (let i=0;i<symbolsFound;i++) {
          color[0] = Math.floor(Math.random()*360);
          let colorHSL = 'hsl('+color[0]+','+color[1]+'%,'+color[2]+'%)'; //the first value of HSL is an angle -> no percent sign!
          this.cards.push(new Card(this.images[symbolIndexes[i]],cards,colorHSL)); //first
          this.cards.push(new Card(this.images[symbolIndexes[i]],cards,colorHSL)); //second  
        };
        
        //randomize the cards using Durstenfeld shuffle algorythm (props: https://stackoverflow.com/a/12646864)
        for (let i = this.cards.length - 1;i > 0;i--) {
          const j = Math.floor(Math.random() * (i + 1));
          [this.cards[i],this.cards[j]] = [this.cards[j],this.cards[i]];
        }
        this.cards.forEach(function(item,index,array){item.draw();});
        this.moveCounter = document.getElementsByClassName("moves")[0];
        this.moveCounter.innerHTML = this.moves;
        this.changeStateTo('idle');
      }
    },
    'idle':{
      cardClick:function(card){
        console.log("transition: flip1st");
        card.flipFront();
        this.firstCard = card;
        this.changeStateTo('oneCardFlipped');
      },
      finish:function(){
        console.log("transition:finish");
        let finalMoveCount = document.getElementsByClassName('final-move-count')[0];
        finalMoveCount.innerHTML = this.moves;
        this.setScreenTo('end');
        this.changeStateTo('end');
        document.getElementsByClassName('endbox__button')[0].addEventListener('click',function(event) {
          game.dispatch('click');
        });
      }
    },
    'oneCardFlipped':{
      cardClick:function(card){
        console.log("transition: flip2nd");
        this.secondCard = card;
        this.secondCard.flipFront();
        this.changeStateTo('matching');
        game.dispatch('matchCards');
      }
    },
    'matching':{
      'matchCards':function(){
        console.log("state: matching cards");
        window.setTimeout(function(){
          if (this.firstCard.symbol == this.secondCard.symbol) {
            console.log("yes!");
            this.firstCard.remove();
            this.secondCard.remove();
            this.firstCard = null;
            this.secondCard = null;
            this.cardsLeft--;
            this.changeStateTo('idle');
            console.log(this.cardsLeft);
            if (this.cardsLeft == 0) {
              console.log("no cards left");
              game.dispatch('finish');
            }
          } else {
            console.log("no");
            this.firstCard.flipBack();
            this.secondCard.flipBack();
            this.firstCard = null;
            this.secondCard = null;
            this.changeStateTo('idle');
          }          
        }.bind(this),1000); 
      }    
    },
    'end':{
      click:function(){
        console.log("transition: reset");
        this.changeStateTo('intro');
        game.dispatch("click");
      }
    },
      
  }
}
/*
State machines consist of STATES and TRANSITIONS. States are stable and wait for input, transitions process data and then switch to a state. EVENTS are what triggers transitions.

In this game, there are these STATES: 
* init - initial game state
* intro - intro text; waiting for button click
* idle -- waits for a card to be flipped
* oneCardFlipped -- waits for 2nd card to be flipped
* end - score card and reset button

This game has these TRANSITIONS:
* setup - from init to intro, draws the first screen
* dealing - from intro to idle, cards being laid out
* flip1st - from idle to oneCardFlipped
* flip2nd - from oneCardFlipped to matching
* matching - matches the flipped cards and removes them or flips them back; if all cards are flipped, it triggers the finish transition
* finish - from oneCardFlipped to end; draws the end  screen
* reset - start a new game

*/

game.changeStateTo('init');
game.dispatch('setup');



              
            
!
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