Code

library_books<canvas id="canvas" width="200" height="200" style="background-color: #f9f9f9;cursor:pointer;"></canvas>

<script>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var speed=5,
    y=50,
    animation;

function draw() {
  ctx.clearRect(0,0, canvas.width, canvas.height);
  ctx.beginPath();
  ctx.arc(100, y, 15, 0, Math.PI * 2, true);
  ctx.stroke();

  y+=speed;
  //Bound the canvas area
  if (y+speed > canvas.height-15 || y+speed <25) speed = -speed;

  animation = requestAnimationFrame(draw);
}

canvas.addEventListener('mouseover', function() {
  animation = requestAnimationFrame(draw);
});

canvas.addEventListener('mouseout', function() {
  cancelAnimationFrame(animation);
});
</script>