jQuery插件floatIt，浮动div并居中在上方或者下方

网上找的太重量级了，写了个轻量级的。满足自己的需求就好，以后再加各种浮动，比如右下角之类的。

/*
* jQuery float it plugin
* Version 1.0 (8-July-2010)
* @requires jQuery v1.4 or later
*
* Copyright (c) 2009-2010 Tony ZHOU
* Dual licensed under the MIT and GPL licenses:
*/

jQuery.fn.floatIt = function (options) {
//parameter like { location: "bottom" } or { location: "top" }
// by extending the default settings, we don't modify the argument
settings = jQuery.extend({ location: "bottom" }, options);

var h = $(window).height();
var w = $(window).width();

var topLocation = 0;
var leftLocation = w / 2 - $(this).width()/2;

var currentId = $(this).attr("id");

switch (settings["location"].toLowerCase()) {
case ("bottom"):
topLocation = h - $(this).width();
$(window).scroll(function () {
var topLocation = $(document).scrollTop() + $(window).height() - $("#" + currentId).height(); //closure
$("#" + currentId).css({ position: "absolute", top: topLocation, left: leftLocation });
});
break;
case ("top"):
topLocation = 0;
$(window).scroll(function () {
var topLocation = $(document).scrollTop(); //closure
$("#" + currentId).css({ position: "absolute", top: topLocation, left: leftLocation });
});
break;
default:
topLocation = h - $(this).width();
break;
}

$(this).css({ position: "absolute", top: topLocation, left: leftLocation });
};