source.html

<pre id="e" style="transform:scaleY(.5);text-align:center">
<script>
	var fieldSize = 14, s = ' ', b = 0, n = "\n", direction, newDirection, snake = curtain = [], foodX, foodY, timer, m = Math, d = m.random, reset = clearInterval, launch = setInterval, content = 'innerHTML';

	r = (n, f) => {
		for (j = 0; j++ < n; f(j));
	};
	
	t = t => e[content] += t;
	
	redraw = _ => {
		e[content] = n;
		r(fieldSize + 2, _ => t(b)); t(n);
		for (y = fieldSize - 1; y >= 0; y--) {
			t(b);
			for (x = 0; x <= fieldSize - 1; x++)
				isSnakeAtCoordinates(x, y) || foodX == x && foodY == y || ~curtain.indexOf(y) ? t(b) : t(s);
			t(b); t(n);
		}
		r(fieldSize + 2, _ => t(b));
	};
	
	onkeydown = event => {
		/*
		keycodes | constant (=code-36) | direction
		37 | 1 | left
		38 | 2 | up
		39 | 3 | right
		40 | 4 | down
		*/
		temp = event.keyCode - 36;
		if (m.abs(temp - direction) != 2)
			newDirection = temp;
	};
	
	coordinateLoopIncrement = crd => crd == fieldSize - 1 ? 0 : crd + 1;

	coordinateLoopDecrement = crd => crd == 0 ? fieldSize - 1 : crd - 1;

	step = _ => {
		if (newDirection) {
			direction = newDirection;
			newDirection = 0;
		}
		
		newX = snake[0][0];
		newY = snake[0][1];

		if (direction == 1) newX = coordinateLoopDecrement(newX);
		if (direction == 2) newY = coordinateLoopIncrement(newY);
		if (direction == 3) newX = coordinateLoopIncrement(newX);
		if (direction == 4) newY = coordinateLoopDecrement(newY);
		
		if (!isSnakeAtCoordinates(newX, newY)) {
			snake.unshift([newX, newY]);
			snake[0][0] == foodX && snake[0][1] == foodY ? addFood() : snake.pop();
		} else {
			restart(reset(timer));
		}
		
	};

	isSnakeAtCoordinates = (x, y) => {
		for (k = 0; k < snake.length; k++)
			if (snake[k][0] == x && snake[k][1] == y) return 1;
		
	};

	getRandomCoordinate = _ => ~~(d() * (fieldSize - 1));

	addFood = _ => {
		do {
			foodX = getRandomCoordinate();
			foodY = getRandomCoordinate();
		} while (isSnakeAtCoordinates(foodX, foodY));
	};

	prepareField = _ => {
		snake = [];
		direction = 3;
		r(3, (i)=>(snake.push([~~(fieldSize/2-i), ~~(fieldSize/2)])));
		addFood();
		redraw();
	};

	startGame = _ => {
		timer = launch(() => {
			step();
			redraw();
		}, 150);
	};
	
	startGame(prepareField());
	
	restart = _ => {
		l = 0;
		up = 1;
		timer = launch(() => {
			redraw();
			if (up) {
				curtain.push(l);
				l++;
				if (l == fieldSize) up = 0;
			} else {
				if (l == fieldSize) prepareField();
				curtain.pop();
				l--;
				if (!l) {
					startGame(reset(timer));
				}
			}
		}, 20);
	};
</script>