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HTML

              
                p.text-debug This pen is supposed to overwrite the favicon, if you don't see it, <a href="https://codepen.io/jibhaine/debug/Boqmpe"  target="_blank">click here</a> 
p.text-help use the arrow keys : left/right to move, up/down to rotate, space to get the piece down
canvas#c
              
            
!

CSS

              
                body{
  width:100%;
  height:100%;
  overflow:hidden;
  background-color:#333;
}
canvas{
  position:absolute;
  left:50%;
  top:50%;
  margin-left:-8px;
  margin-top:-8px;
}
p{
  font-family:courier;
  font-size:.75em;
  margin:.75em;
  color:white;
  text-shadow:1px 1px 2px black;
}
p.text-debug{
  top:1.5em;
}
a{color:white;font:bold;}
              
            
!

JS

              
                const
//board size in number of tiles.
  BOARD_WIDTH = 16,
  BOARD_HEIGHT = 16,
  //tiles size (each tile is a square so only one)
  TILE_SIZE = 1,
  TETRAMINOS = [{
    name: 'I',
    color: '#00FFFF',
    shape: [
      [1],
      [1],
      [1],
      [1]
    ]
  }, {
    name: 'O',
    color: '#FFD800',
    shape: [
      [1, 1],
      [1, 1]
    ]
  }, {
    name: 'T',
    color: '#B200FF',
    shape: [
      [1, 1, 1],
      [0, 1, 0]
    ]
  }, {
    name: 'S',
    color: '#4CFF00',
    shape: [
      [1, 0],
      [1, 1],
      [0, 1]
    ]
  }, {
    name: 'Z',
    color: '#FF0000',
    shape: [
      [0, 1],
      [1, 1],
      [1, 0]
    ]
  }, {
    name: 'J',
    color: '#0066ff',
    shape: [
      [0, 1],
      [0, 1],
      [1, 1]
    ]
  }, {
    name: 'L',
    color: '#FF6A00',
    shape: [
      [1, 0],
      [1, 0],
      [1, 1]
    ]
  }];
//globals
let
  canvas = document.getElementById('c'),
  context = canvas.getContext('2d'),
  board = undefined,
  collisions = undefined,
  gameSpeed = 30, //number of frames between each tick.
  frameCount = 0;
/**
 * Shape, initialized from TETRAMINOS constant.
 */
class Shape {
  constructor(x, y, baseShape) {
    this.x = x;
    this.y = y;
    this.shape = baseShape.shape.slice();
    this.color = baseShape.color;
  }
  render(context) {
    context.fillStyle = this.color;

    for (let i = 0; i < this.shape.length; i++) {
      for (let j = 0; j < this.shape[i].length; j++) {
        if (this.shape[i][j]) {
          context.fillRect(
            (this.x + i) * TILE_SIZE,
            (this.y + j) * TILE_SIZE,
            TILE_SIZE,
            TILE_SIZE
          );
        }
      }
    }
    context.fillStyle = '#000000';
  }
}
/**
 * contains fixed tiles and moving pieces
 */
class Board {
  constructor() {
    //moving piece
    this.currentShape = {};
    //array of colors (non-moving shapes)
    this.tiles = [];
    this.initialize();
  }
  initialize() {
    for (let x = 0; x < BOARD_WIDTH; x++) {
      this.tiles[x] = [];
      for (let y = 0; y < BOARD_HEIGHT; y++) {
        this.tiles[x][y] = 0;
      }
    }
  }
  render() {
    context.fillStyle = '#000000';
    context.fillRect(0, 0,
      BOARD_WIDTH * TILE_SIZE,
      BOARD_HEIGHT * TILE_SIZE
    )
    //draw already placed tiles
    for (let x = 0; x < BOARD_WIDTH; x++) {
      for (let y = 0; y < BOARD_HEIGHT; y++) {
        if(this.tiles[x][y]){
          context.fillStyle = this.tiles[x][y];
          context.fillRect(
            x * TILE_SIZE,
            y * TILE_SIZE,
            TILE_SIZE,
            TILE_SIZE
          ); 
        }
      }
    }
    //Draw current moving shape
    this.currentShape.render(context);
  }
  fixShape() {
    for (let x = 0; x < this.currentShape.shape.length; x++) {
      for (let y = 0; y < this.currentShape.shape[0].length; y++) {
        if (this.currentShape.shape[x][y] !== 0) {
          //fix shape in tiles array
          this.tiles[this.currentShape.x + x][this.currentShape.y + y] = this.currentShape.color;
        }
      }
    }
  }
  detectFullLines() {
    let fullLineIndexes = [];
    for (let y = 0; y < BOARD_HEIGHT; y++) {
      let isFull = true;
      for (let x = 0; x < BOARD_WIDTH; x++) {
        if(this.tiles[x][y] == 0){
          isFull = false;
        }
      }
      if(isFull){
        fullLineIndexes.push(y);
      }
    }
    for(let index of fullLineIndexes){
      this.collapseLine(index);
    }
  }
  collapseLine(index){
    for (let y = index; y > 0; y--) {
      for (let x = 0; x < BOARD_WIDTH; x++) {
        this.tiles[x][y] = this.tiles[x][y-1];
      }
    }
  }
}

/**
 * Uses the Board.tiles to check for collisions.
 * Principle : create a new shape at future potential position and check for collision/out of bounds
 */
class CollisionDetector {
  constructor(currentBoard) {
    this.board = currentBoard;
    this.nextShape = {};
  }
  /**
   * clone currentShape to nextShape
   */
  initNextShape() {
    Object.assign(this.nextShape, this.board.currentShape);
    //avoid keeping reference of nested shape array.
    Object.assign(this.nextShape.shape, this.board.currentShape.shape);
  }
  /**
   * for each plain cell of the shape, check if an existing tiles exists at the position
   */
  willItCollide() {
    let collisionOccured = false;
    for (let x = 0; x < this.nextShape.shape.length; x++) {
      for (let y = 0; y < this.nextShape.shape[0].length; y++) {
        if (this.nextShape.shape[x][y] !== 0 && this.board.tiles[this.nextShape.x + x][this.nextShape.y + y] !== 0) {
          //bingo !
          collisionOccured = true;
        }
      }
    }
    return collisionOccured;
  }
  /**
  * for each cell of the shape, checks if we are still inside
  */
  willBeOutOfBounds(){
    let outOfBounds = false;
    for (let x = 0; x < this.nextShape.shape.length; x++) {
      for (let y = 0; y < this.nextShape.shape[0].length; y++) {
        if(this.nextShape.shape[x][y] !== 0){
          //real position
          let i = this.nextShape.x + x;
          let j = this.nextShape.y + y;
          outOfBounds &= i < 0 && i >= BOARD_WIDTH && j < 0 && j >= BOARD_HEIGHT;
        }
      }
    }
    
    return outOfBounds;
  }
  canMoveDown() {
    let reachedTheBottom = (this.board.currentShape.shape[0].length + this.board.currentShape.y < BOARD_HEIGHT);
    this.initNextShape();
    this.nextShape.y++;
    return reachedTheBottom && !this.willItCollide();
  }
  canMoveLeft() {
    let reachedLeftBorder = (this.board.currentShape.x > 0);
    this.initNextShape();
    this.nextShape.x--;
    return reachedLeftBorder && !this.willItCollide();
  }
  canMoveRight() {
    let reachedRightBorder = (this.board.currentShape.x + this.board.currentShape.shape.length < BOARD_WIDTH);
    this.initNextShape();
    this.nextShape.x++;
    return reachedRightBorder && !this.willItCollide();
  }
  canRotateLeft() {
    this.initNextShape();
    this.nextShape.shape = Rotator.toTheLeft(this.nextShape.shape);
    return !this.willBeOutOfBounds() && !this.willItCollide();
  }
  canRotateRight() {
    this.initNextShape();
    this.nextShape.shape = Rotator.toTheRight(this.nextShape.shape);
    return !this.willBeOutOfBounds() && !this.willItCollide();
  }
}

/**
 * Utility methods to rotate an array.
 */
class Rotator{
  
  /**
   * Transpose bi-dimensional array
   */
  static transpose(m){
    let result = new Array(m[0].length);
    for (let i = 0; i < m[0].length; i++) {
      result[i] = new Array(m.length - 1);
      for (let j = m.length - 1; j > -1; j--) {
        result[i][j] = m[j][i];
      }
    }
    return result;
  }
  /**
   * rotate : transpose then reverse,
   * @see http://stackoverflow.com/questions/42519/how-do-you-rotate-a-two-dimensional-array
   */
  static toTheLeft(m) {
    return this.transpose(m).reverse();;
  }
  /**
   *  reverse, then transpose
   */
  static toTheRight(m) {
    return this.transpose(m.reverse());
  }
}

let
  /**
   * Creates a new random tetramino.
   */
  shapeFactory = () => {
    let i = Math.floor(Math.random() * TETRAMINOS.length);
    //console.log('new shape from base : ',TETRAMINOS[i]);
    //new random tetramino at the top center.
    return new Shape(BOARD_WIDTH / 2 - 1, 0, TETRAMINOS[i]);
  },
  /**
   * game logic.
   */
  tick = () => {
    if (collisions.canMoveDown()) {
      //go down
      board.currentShape.y++;
      board.detectFullLines();
    } else {
      board.fixShape();
      board.currentShape = shapeFactory();
      //end of game if the new shape can't go down
      if (!collisions.canMoveDown()) {
        initialize();
      }
    }
    faviconize();
  },
  animate = () => {
    board.render();
    //todo extract in a setInterval or wathever, this makes the speed go batsheetcray
    if (frameCount % gameSpeed == 0) {
      tick();
    }
    frameCount++;
    requestAnimationFrame(animate);
  },
  initialize = () => {
    canvas.width = BOARD_WIDTH * TILE_SIZE;
    canvas.height = BOARD_HEIGHT * TILE_SIZE;
    frameCount = 0;
    board = new Board();
    board.currentShape = shapeFactory();
    collisions = new CollisionDetector(board);
    animate();
    //remove the fullscreen link if we are in debug view
    if(/(.*)\/debug(.*)/g.test(document.location)){
      document.querySelector('.text-debug').style.display = 'none';
    }
  },
  
  keyHandler = (event) => {
    let e = event || window.event;
    // up arrow
    if (e.keyCode == '38') {
      if (collisions.canRotateLeft()) {
        board.currentShape.shape = Rotator.toTheLeft(board.currentShape.shape);
      }
    }
    // down arrow
    else if (e.keyCode == '40') {
      if (collisions.canRotateRight()) {
        board.currentShape.shape = Rotator.toTheRight(board.currentShape.shape);
      }

    }
    // left arrow
    else if (e.keyCode == '37') {
      if (collisions.canMoveLeft()) {
        board.currentShape.x--;
      }
    } 
    // right arrow
    else if (e.keyCode == '39') {
      if (collisions.canMoveRight()) {
        board.currentShape.x++;
      }
    } 
    //space bar
    else if (e.keyCode == '32' || e.keyCode == ' ') {

      while (collisions.canMoveDown()) {
        //go down
        board.currentShape.y++;
      }
    }

  },
  /**
   * Creates a favicon element and add it ot the dom.
   */
  linkFactory = () => {
    let link = document.createElement('link');
    link.type = 'image/x-icon';
    link.rel = 'shortcut icon';
    document.getElementsByTagName('head')[0].appendChild(link);
    return link;
  },
  /**
   * converts canvas to dataUrl image and sets it as a favicon
   */
  faviconize = () => {
    let link = document.querySelector("link[rel='shortcut icon']");
    if (!link) {
      link = linkFactory();
    }
    link.href = canvas.toDataURL("image/x-icon");

  };

document.addEventListener('DOMContentLoaded', initialize);
document.addEventListener('keydown', keyHandler);


//polyfill for Object.assign taken from here : https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
if (typeof Object.assign != 'function') {
  Object.assign = function(target) {
    'use strict';
    if (target == null) {
      throw new TypeError('Cannot convert undefined or null to object');
    }

    target = Object(target);
    for (var index = 1; index < arguments.length; index++) {
      var source = arguments[index];
      if (source != null) {
        for (var key in source) {
          if (Object.prototype.hasOwnProperty.call(source, key)) {
            target[key] = source[key];
          }
        }
      }
    }
    return target;
  };
}
              
            
!
999px

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