script.js

var blockSize = 25;
var total_row = 17; //total row number
var total_col = 17; //total column number
var board;
var context;

var snakeX = blockSize * 5;
var snakeY = blockSize * 5;

// Set the total number of rows and columns
var speedX = 0; //speed of snake in x coordinate.
var speedY = 0; //speed of snake in Y coordinate.

var snakeBody = [];

var foodX;
var foodY;

var gameOver = false;

window.onload = function () {
  // Set board height and width
  board = document.getElementById("board");
  board.height = total_row * blockSize;
  board.width = total_col * blockSize;
  context = board.getContext("2d");

  placeFood();
  document.addEventListener("keyup", changeDirection); //for movements
  // Set snake speed
  setInterval(update, 1000 / 5);
};

function update() {
  if (gameOver) {
    return;
  }

  // Background of a Game
  context.fillStyle = "green";
  context.fillRect(0, 0, board.width, board.height);

  // Set food color and position
  context.fillStyle = "yellow";
  context.fillRect(foodX, foodY, blockSize, blockSize);

  if (snakeX == foodX && snakeY == foodY) {
    snakeBody.push([foodX, foodY]);
    placeFood();
  }

  // body of snake will grow
  for (let i = snakeBody.length - 1; i > 0; i--) {
    // it will store previous part of snake to the current part
    snakeBody[i] = snakeBody[i - 1];
  }
  if (snakeBody.length) {
    snakeBody[0] = [snakeX, snakeY];
  }

  context.fillStyle = "white";
  snakeX += speedX * blockSize; //updating Snake position in X coordinate.
  snakeY += speedY * blockSize; //updating Snake position in Y coordinate.
  context.fillRect(snakeX, snakeY, blockSize, blockSize);
  for (let i = 0; i < snakeBody.length; i++) {
    context.fillRect(snakeBody[i][0], snakeBody[i][1], blockSize, blockSize);
  }

  if (
    snakeX < 0 ||
    snakeX > total_col * blockSize ||
    snakeY < 0 ||
    snakeY > total_row * blockSize
  ) {
    // Out of bound condition
    gameOver = true;
    alert("Game Over");
  }

  for (let i = 0; i < snakeBody.length; i++) {
    if (snakeX == snakeBody[i][0] && snakeY == snakeBody[i][1]) {
      // Snake eats own body
      gameOver = true;
      alert("Game Over");
    }
  }
}

// Movement of the Snake - We are using addEventListener
function changeDirection(e) {
  if (e.code == "ArrowUp" && speedY != 1) {
    // If up arrow key pressed with this condition...
    // snake will not move in the opposite direction
    speedX = 0;
    speedY = -1;
  } else if (e.code == "ArrowDown" && speedY != -1) {
    //If down arrow key pressed
    speedX = 0;
    speedY = 1;
  } else if (e.code == "ArrowLeft" && speedX != 1) {
    //If left arrow key pressed
    speedX = -1;
    speedY = 0;
  } else if (e.code == "ArrowRight" && speedX != -1) {
    //If Right arrow key pressed
    speedX = 1;
    speedY = 0;
  }
}

// Randomly place food
function placeFood() {
  // in x coordinates.
  foodX = Math.floor(Math.random() * total_col) * blockSize;

  //in y coordinates.
  foodY = Math.floor(Math.random() * total_row) * blockSize;
}