canvas005

HTML

<canvas width="500" height="500" id="canvas"></canvas>

JavaScript

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var i=0;
var mouseY;
setTimeout(function(){
    ctx.clearRect(0,0,500,500);
    ctx.fillRect(mouseY,0,100,100);
    setTimeout(arguments.callee, 20);
},1);

$(window).mousemove(function(){
   mouseY = this.pageX;
});