Tips and Tricks - HTML5 Animation with JavaScript - page 450

<source src="boing.mp3" />
<p>This browser does not support the <code>audio</code> element.</p>
</audio>
<script src="utils.js"></script>
<script src="ball.js"></script>
<script>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
sound = document.getElementById('sound'),
ball = new Ball(),
vx = Math.random() * 10 - 5,
vy = Math.random() * 10 - 5,
bounce = -0.7;
//the animation only runs with audio
if (typeof sound !== 'object' || !sound.canPlayType) {
throw new Error("This browser does not support the audio element.");
}
(function drawFrame () {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
var left = 0,
right = canvas.width,
top = 0,
bottom = canvas.height;
ball.x += vx;
ball.y += vy;
if (ball.x + ball.radius > right) {
sound.play();
ball.x = right - ball.radius;
vx *= bounce;
} else if (ball.x - ball.radius < left) {
sound.play();
ball.x = left + ball.radius;
vx *= bounce;
}
if (ball.y + ball.radius > bottom) {
sound.play();
ball.y = bottom - ball.radius;
vy *= bounce;
} else if (ball.y - ball.radius < top) {
sound.play();
ball.y = top + ball.radius;
vy *= bounce;
}
ball.draw(context);
}());
};