js game code example

Example 1: how to create a game in html

<!-- A SIMPLE SNAKE GAME MADE BY HTML AND CSS -->

<!DOCTYPE html>
<html>
<head>
  <title></title>
  <style>
  html, body {
    height: 100%;
    margin: 0;
  }

  body {
    background: black;
    display: flex;
    align-items: center;
    justify-content: center;
  }
  canvas {
    border: 1px solid white;
  }
  </style>
</head>
<body>
<canvas width="400" height="400" id="game"></canvas>
<script>
var canvas = document.getElementById('game');
var context = canvas.getContext('2d');

var grid = 16;
var count = 0;
  
var snake = {
  x: 160,
  y: 160,
  
  // snake velocity. moves one grid length every frame in either the x or y direction
  dx: grid,
  dy: 0,
  
  // keep track of all grids the snake body occupies
  cells: [],
  
  // length of the snake. grows when eating an apple
  maxCells: 4
};
var apple = {
  x: 320,
  y: 320
};

// get random whole numbers in a specific range
// @see https://stackoverflow.com/a/1527820/2124254
function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min)) + min;
}

// game loop
function loop() {
  requestAnimationFrame(loop);

  // slow game loop to 15 fps instead of 60 (60/15 = 4)
  if (++count < 4) {
    return;
  }

  count = 0;
  context.clearRect(0,0,canvas.width,canvas.height);

  // move snake by it's velocity
  snake.x += snake.dx;
  snake.y += snake.dy;

  // wrap snake position horizontally on edge of screen
  if (snake.x < 0) {
    snake.x = canvas.width - grid;
  }
  else if (snake.x >= canvas.width) {
    snake.x = 0;
  }
  
  // wrap snake position vertically on edge of screen
  if (snake.y < 0) {
    snake.y = canvas.height - grid;
  }
  else if (snake.y >= canvas.height) {
    snake.y = 0;
  }

  // keep track of where snake has been. front of the array is always the head
  snake.cells.unshift({x: snake.x, y: snake.y});

  // remove cells as we move away from them
  if (snake.cells.length > snake.maxCells) {
    snake.cells.pop();
  }

  // draw apple
  context.fillStyle = 'red';
  context.fillRect(apple.x, apple.y, grid-1, grid-1);

  // draw snake one cell at a time
  context.fillStyle = 'green';
  snake.cells.forEach(function(cell, index) {
    
    // drawing 1 px smaller than the grid creates a grid effect in the snake body so you can see how long it is
    context.fillRect(cell.x, cell.y, grid-1, grid-1);  

    // snake ate apple
    if (cell.x === apple.x && cell.y === apple.y) {
      snake.maxCells++;

      // canvas is 400x400 which is 25x25 grids 
      apple.x = getRandomInt(0, 25) * grid;
      apple.y = getRandomInt(0, 25) * grid;
    }

    // check collision with all cells after this one (modified bubble sort)
    for (var i = index + 1; i < snake.cells.length; i++) {
      
      // snake occupies same space as a body part. reset game
      if (cell.x === snake.cells[i].x && cell.y === snake.cells[i].y) {
        snake.x = 160;
        snake.y = 160;
        snake.cells = [];
        snake.maxCells = 4;
        snake.dx = grid;
        snake.dy = 0;

        apple.x = getRandomInt(0, 25) * grid;
        apple.y = getRandomInt(0, 25) * grid;
      }
    }
  });
}

// listen to keyboard events to move the snake
document.addEventListener('keydown', function(e) {
  // prevent snake from backtracking on itself by checking that it's 
  // not already moving on the same axis (pressing left while moving
  // left won't do anything, and pressing right while moving left
  // shouldn't let you collide with your own body)
  
  // left arrow key
  if (e.which === 37 && snake.dx === 0) {
    snake.dx = -grid;
    snake.dy = 0;
  }
  // up arrow key
  else if (e.which === 38 && snake.dy === 0) {
    snake.dy = -grid;
    snake.dx = 0;
  }
  // right arrow key
  else if (e.which === 39 && snake.dx === 0) {
    snake.dx = grid;
    snake.dy = 0;
  }
  // down arrow key
  else if (e.which === 40 && snake.dy === 0) {
    snake.dy = grid;
    snake.dx = 0;
  }
});

// start the game
requestAnimationFrame(loop);
</script>
</body>
</html>

Example 2: how to create a game using javascript

<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<style>
canvas {
    border:1px solid #d3d3d3;
    background-color: #f1f1f1;
}
</style>
</head>
<body onload="startGame()">
<script>

var myGamePiece;
var myObstacles = [];
var myScore;

function startGame() {
    myGamePiece = new component(30, 30, "red", 10, 120);
    myGamePiece.gravity = 0.05;
    myScore = new component("30px", "Consolas", "black", 280, 40, "text");
    myGameArea.start();
}

var myGameArea = {
    canvas : document.createElement("canvas"),
    start : function() {
        this.canvas.width = 480;
        this.canvas.height = 270;
        this.context = this.canvas.getContext("2d");
        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.frameNo = 0;
        this.interval = setInterval(updateGameArea, 20);
        },
    clear : function() {
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
    }
}

function component(width, height, color, x, y, type) {
    this.type = type;
    this.score = 0;
    this.width = width;
    this.height = height;
    this.speedX = 0;
    this.speedY = 0;    
    this.x = x;
    this.y = y;
    this.gravity = 0;
    this.gravitySpeed = 0;
    this.update = function() {
        ctx = myGameArea.context;
        if (this.type == "text") {
            ctx.font = this.width + " " + this.height;
            ctx.fillStyle = color;
            ctx.fillText(this.text, this.x, this.y);
        } else {
            ctx.fillStyle = color;
            ctx.fillRect(this.x, this.y, this.width, this.height);
        }
    }
    this.newPos = function() {
        this.gravitySpeed += this.gravity;
        this.x += this.speedX;
        this.y += this.speedY + this.gravitySpeed;
        this.hitBottom();
    }
    this.hitBottom = function() {
        var rockbottom = myGameArea.canvas.height - this.height;
        if (this.y > rockbottom) {
            this.y = rockbottom;
            this.gravitySpeed = 0;
        }
    }
    this.crashWith = function(otherobj) {
        var myleft = this.x;
        var myright = this.x + (this.width);
        var mytop = this.y;
        var mybottom = this.y + (this.height);
        var otherleft = otherobj.x;
        var otherright = otherobj.x + (otherobj.width);
        var othertop = otherobj.y;
        var otherbottom = otherobj.y + (otherobj.height);
        var crash = true;
        if ((mybottom < othertop) || (mytop > otherbottom) || (myright < otherleft) || (myleft > otherright)) {
            crash = false;
        }
        return crash;
    }
}

function updateGameArea() {
    var x, height, gap, minHeight, maxHeight, minGap, maxGap;
    for (i = 0; i < myObstacles.length; i += 1) {
        if (myGamePiece.crashWith(myObstacles[i])) {
            return;
        } 
    }
    myGameArea.clear();
    myGameArea.frameNo += 1;
    if (myGameArea.frameNo == 1 || everyinterval(150)) {
        x = myGameArea.canvas.width;
        minHeight = 20;
        maxHeight = 200;
        height = Math.floor(Math.random()*(maxHeight-minHeight+1)+minHeight);
        minGap = 50;
        maxGap = 200;
        gap = Math.floor(Math.random()*(maxGap-minGap+1)+minGap);
        myObstacles.push(new component(10, height, "green", x, 0));
        myObstacles.push(new component(10, x - height - gap, "green", x, height + gap));
    }
    for (i = 0; i < myObstacles.length; i += 1) {
        myObstacles[i].x += -1;
        myObstacles[i].update();
    }
    myScore.text="SCORE: " + myGameArea.frameNo;
    myScore.update();
    myGamePiece.newPos();
    myGamePiece.update();
}

function everyinterval(n) {
    if ((myGameArea.frameNo / n) % 1 == 0) {return true;}
    return false;
}

function accelerate(n) {
    myGamePiece.gravity = n;
}
</script>
<br>
<button onmousedown="accelerate(-0.2)" onmouseup="accelerate(0.05)">ACCELERATE</button>
<p>Use the ACCELERATE button to stay in the air</p>
<p>How long can you stay alive?</p>
</body>
</html>

Example 3: how to make a javascript game

//Javascript game template
//Move player with arrow keys

var canvas = document.createElement("canvas");
canvas.width = 500;
canvas.height = 500;
document.body.appendChild(canvas);
var ctx = canvas.getContext("2d");

var player = {x: canvas.width / 2, y: canvas.height / 2, speed: 10};
var keys = [];

function update() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  
  ctx.beginPath();
  ctx.fillStyle = "red";
  ctx.fillRect(player.x, player.y, 50, 50);
  
  if (keys[37])
    player.x -= player.speed;
  if (keys[38])
    player.y -= player.speed;
  if (keys[39])
    player.x += player.speed;
  if (keys[40])
    player.y += player.speed;
  
  requestAnimationFrame(update);
}
update();

document.onkeydown = function(e) {
  keys[e.keyCode] = true;
}
document.onkeyup = function(e) {
  keys[e.keyCode] = false;
}

Example 4: javascript making a tag game

(function)game=tag
(function)=character=109
(function)=vehicles=200

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