tetris.js/tetris.js

const canvas = document.getElementById('tetris');
const context = canvas.getContext('2d');

const fieldSize = {x: 12, y: 20};

let isPaused = true;

function clearScreen() {
    context.clearRect(0, 0, canvas.width, canvas.height);
}

function arenaSweep() {
    let rowCount = 1;
    outer: for (let y = arena.length - 1; y > 0; --y) {
        for (let x = 0; x < arena[y].length; ++x) {
            if (arena[y][x] === 0) {
                continue outer;
            }
        }

        const row = arena.splice(y, 1)[0].fill(0);
        arena.unshift(row);
        ++y;

        player.score += rowCount * 10;
        rowCount *= 2;
    }
    dropInterval -= player.score / 10;
    dropInterval = dropInterval > 50 ? dropInterval : 50;
}

function collide(arena, player) {
    const [m, o] = [player.matrix, player.pos];
    for (let y = 0; y < m.length; ++y) {
        for (let x = 0; x < m[y].length; ++x) {
            if (m[y][x] !== 0 && (arena[y + o.y] && arena[y + o.y][x + o.x]) !== 0) {
                return true;
            }
        }
    }
    return false;
}

function createMatrix(w, h) {
    const matrix = [];
    while (h--) {
        matrix.push(new Array(w).fill(0));
    }
    return matrix;
}

function createPiece(type) {
    switch (type) {
        case 'T':
            return [
                [0, 0, 0],
                [1, 1, 1],
                [0, 1, 0]
            ];
        case 'O':
            return [
                [2, 2],
                [2, 2]
            ];
        case 'J':
            return [
                [0, 3, 0],
                [0, 3, 0],
                [3, 3, 0]
            ];
        case 'L':
            return [
                [0, 4, 0],
                [0, 4, 0],
                [0, 4, 4]
            ];
        case 'I':
            return [
                [0, 0, 5, 0],
                [0, 0, 5, 0],
                [0, 0, 5, 0],
                [0, 0, 5, 0]
            ];
        case 'S':
            return [
                [0, 6, 6],
                [6, 6, 0],
                [0, 0, 0]
            ];
        case 'Z':
            return [
                [7, 7, 0],
                [0, 7, 7],
                [0, 0, 0]
            ];
    }
}

function draw() {
    context.fillStyle = '#000';
    context.fillRect(0, 0, canvas.width, canvas.height);

    drawMatrix(arena, {x: 0, y: 0});
    drawMatrix(player.matrix, player.pos);
}

function drawMatrix(matrix, offset) {
    matrix.forEach((row, y) => {
        row.forEach((value, x) => {
            if (value !== 0) {
                context.fillStyle = colors[value];
                context.fillRect(x + offset.x, y + offset.y, 1, 1);
            }
        });
    });
}

function merge(arena, player) {
    player.matrix.forEach((row, y) => {
        row.forEach((value, x) => {
            if (value !== 0) {
                arena[y + player.pos.y][x + player.pos.x] = value;
            }
        });
    });
}

function playerDrop() {
    player.pos.y++;
    if (collide(arena, player)) {
        player.pos.y--;
        merge(arena, player);
        playerReset();
        arenaSweep();
        updateScore();
    }
    dropCounter = 0;
}

function playerMove(dir) {
    player.pos.x += dir;
    if (collide(arena, player)) {
        player.pos.x -= dir;
    }
}

function playerReset() {
    const pieces = 'IJLOSTZ';
    player.matrix = createPiece(pieces[pieces.length * Math.random() | 0]);
    player.pos.y = 0;
    player.pos.x = (arena[0].length / 2 | 0) - (player.matrix[0].length / 2 | 0);
    if (collide(arena, player)) {
        arena.forEach(row => row.fill(0));
        player.score = 0;
        dropInterval = 1000;
        updateScore();
    }
}

function playerRotate(dir) {
    rotate(player.matrix, dir);

    const pos = player.pos.x;
    let offset = 1;
    while (collide(arena, player)) {
        player.pos.x += offset;
        offset = -(offset + (offset > 0 ? 1 : -1));
        if (offset > player.matrix[0].length) {
            rotate(player.matrix, -dir);
            player.pos.x = pos;
            return;
        }
    }
}

function rotate(matrix, dir) {
    for (let y = 0; y < matrix.length; ++y) {
        for (let x = 0; x < y; ++x) {
            [
                matrix[x][y],
                matrix[y][x]
            ] = [
                matrix[y][x],
                matrix[x][y]
            ];
        }
    }

    if (dir > 0) {
        matrix.forEach(row => row.reverse());
    } else {
        matrix.reverse();
    }
}

let dropCounter = 0;
let dropInterval = 1000;

let lastTime = 0;

function update(time = 0) {
    if(!isPaused) {
        const deltaTime = time - lastTime;
        lastTime = time;

        dropCounter += deltaTime;
        if (dropCounter > dropInterval) {
            playerDrop();
        }

        draw();
        requestAnimationFrame(update);
    }
}

function updateScore() {
    document.getElementById('score').innerText = player.score.toString();
}

const colors = [
    null,
    '#FF0D72',
    '#0DC2FF',
    '#0DFF72',
    '#F538FF',
    '#FF8E0D',
    '#FFE138',
    '#3877FF',
];

let arena = createMatrix(fieldSize.x, fieldSize.y);

const player = {
    pos: {x: 0, y: 0},
    matrix: null,
    score: 0
};

const keys = {
    down: {
        keys: [40, 83],
        action: () => playerDrop()
    },
    left: {
        keys: [37, 65],
        action: () => playerMove(-1)
    },
    right: {
        keys: [39, 68],
        action: () => playerMove(1)
    },
    rotateLeft: {
        keys: [81],
        action: () => playerRotate(-1)
    },
    rotateRight: {
        keys: [69],
        action: () => playerRotate(1)
    }
};

// Keyboard controls
document.addEventListener('keydown', event => {
    Object.keys(keys).map((objKey, index) => {
        const keyBind = keys[objKey];
        if (keyBind.keys.includes(event.keyCode)) {
            keyBind.action();
        }
    });
});

function startGame() {
    arena = createMatrix(fieldSize.x, fieldSize.y)
    playerReset();
    update();
    updateScore();
}