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index.js
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index.js
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const gameBoard = document.querySelector('#gameBoard');
const ctx = gameBoard.getContext("2d");
const scoreText = document.querySelector('#scoreText');
const resetBtn = document.querySelector('#resetBtn');
const gameWidth = gameBoard.width;
const gameHeight = gameBoard.height;
const boardBackground = 'white';
const snakeColor = 'lightgreen';
const snakeBorder = 'black';
const foodColor = 'red';
const unitSize = 25;
let running = false;
let xVelocity = unitSize;
let yVelocity = 0;
let foodX;
let foodY;
let score = 0;
let snake = [
{x: unitSize * 4, y: 0},
{x: unitSize * 3, y: 0},
{x: unitSize * 2, y: 0},
{x: unitSize, y: 0},
{x: 0, y: 0}
];
window.addEventListener('keydown', changeDirection);
resetBtn.addEventListener('click', resetGame);
startGame();
function startGame(){
running = true;
scoreText.textContent = score;
createFood();
drawFood();
nextTick();
}
function nextTick() {
if(running) {
setTimeout(() => {
clearBoard();
drawFood();
moveSnake();
drawSnake();
checkGameOver();
nextTick();
}, 75)
}
else {
displayGameOver();
}
}
function clearBoard() {
ctx.fillStyle = boardBackground;
ctx.fillRect(0, 0, gameWidth, gameHeight)
}
function createFood() {
function randomFood(min, max) {
const randomNumber = Math.round((Math.random() * (max - min) + min) / unitSize) * unitSize;
return randomNumber;
}
foodX = randomFood(0, gameWidth - unitSize);
foodY = randomFood(0, gameWidth - unitSize);
}
function drawFood() {
ctx.fillStyle = foodColor;
ctx.fillRect(foodX, foodY, unitSize, unitSize);
}
function moveSnake() {
const head = {x : snake[0].x + xVelocity, y : snake[0].y + yVelocity}
snake.unshift(head);
// if food is eaten
if(snake[0].x == foodX && snake[0].y == foodY) {
score++;
scoreText.textContent = score;
createFood();
}
else {
snake.pop(head);
}
}
function drawSnake() {
ctx.fillStyle = snakeColor;
ctx.strokeStyle = snakeBorder;
snake.forEach(snakePart => {
ctx.fillRect(snakePart.x, snakePart.y, unitSize, unitSize);
ctx.strokeRect(snakePart.x, snakePart.y, unitSize, unitSize);
})
}
function changeDirection(event) {
const keyPressed = event.keyCode;
const keyUp = 38;
const keyDown = 40;
const keyLeft = 37;
const keyRight = 39;
const goingUp = (yVelocity == -unitSize);
const goingDown = (yVelocity == unitSize);
const goingLeft = (xVelocity == -unitSize);
const goingRight = (xVelocity == unitSize);
switch(true) {
case (keyPressed == keyUp && !goingDown):
yVelocity = -unitSize;
xVelocity = 0;
break;
case (keyPressed == keyDown && !goingUp):
yVelocity = unitSize;
xVelocity = 0;
break;
case (keyPressed == keyLeft && !goingRight):
yVelocity = 0;
xVelocity = -unitSize;
break;
case (keyPressed == keyRight && !goingLeft):
yVelocity = 0;
xVelocity = unitSize;
break;
}
}
function checkGameOver() {
switch(true) {
case (snake[0].x < 0):
running = false;
break;
case (snake[0].x >= gameWidth):
running = false;
break;
case (snake[0].y < 0):
running = false;
break;
case (snake[0].y >= gameHeight):
running = false;
break;
}
for (let i = 1; i < snake.length; i+=1) {
if(snake[i].x == snake[0].x && snake[i].y == snake[0].y) {
running = false;
}
}
}
function displayGameOver() {
ctx.font = '50px MV Boli';
ctx.fillStyle = 'black';
ctx.textAlign = "center";
ctx.fillText("GAME OVER!", gameWidth / 2, gameHeight / 2);
running = false;
}
function resetGame() {
score = 0;
xVelocity = unitSize;
yVelocity = 0;
snake = [
{x: unitSize * 4, y: 0},
{x: unitSize * 3, y: 0},
{x: unitSize * 2, y: 0},
{x: unitSize, y: 0},
{x: 0, y: 0}
];
startGame();
}