Fast Rectangle Intersection Test

<html>
  <head>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
    <title>Fast Rect Intersection Test</title>

    <style type="text/css">
#debug {
    width: 100%;
    height: 50px;
    position: fixed;
    background: #ffffa0;
}

.box {
    position: absolute;
    top: 120px;
    left: 120px;
    width: 50px;
    height: 50px;
    border: 1px solid #aaa;
}
    </style>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>
    <script type="text/javascript">
    <!-- //
 ;
function Rec(ob)
{
    this.lf = ob.offset().left;
    this.tp = ob.offset().top;
    this.rt = this.lf + ob.width();
    this.bt = this.tp + ob.height();

    // this is te core of implementation
    // a scalar test
    this.checkCollision = function( rec )
    {
        if (this.bt >= rec.tp )
            if (this.tp <= rec.bt)
                if (this.rt >= rec.lf)
                    if (this.lf <= rec.rt)
                        return true;
        return false;
    };

    this.toString = function()
    {
        return "["+ this.lf + "," + this.rt + "," + this.tp + "," + this.bt + "," +"]"
    };
    return this;
}

function mouseMove(e)
{
    var s = $("#seeker");
    s.css("top", e.pageY - s.height()*.5).css("left", e.pageX - s.width()*.5);
    var r = new Rec(s);

    $("#debug").html( String((r.checkCollision(r2)) ? "true" : "false") + " " + e.pageX + " " + e.pageY + " " + r.toString());
}

var r2;

function ini()
{
    r2 = new Rec($("#col1"));
    $(window).mousemove(mouseMove);
}

$(window).ready(ini);
    // -->
    </script>
  </head>
  <body>
<div id="debug"></div>
<div class="box" id="col1"></div>
<div class="box" id="seeker"></div>
  </body>
</html>