jQuery检查元素在可滚动div中是否可见

好的，所以我使用以下代码检查元素是否在屏幕上可见。

Ok so I use the following code to check whether an element is visible on-screen.

(function($) {

/**
    * Copyright 2012, Digital Fusion
    * Licensed under the MIT license.
    * http://teamdf.com/jquery-plugins/license/
    *
    * @author Sam Sehnert
    * @desc A small plugin that checks whether elements are within
    *     the user visible viewport of a web browser.
    *     only accounts for vertical position, not horizontal.
 */

$.fn.visible = function(partial) {

    var $t            = $(this),
        $w            = $(window),
        viewTop       = $w.scrollTop(),
        viewBottom    = viewTop + $w.height(),
        _top          = $t.offset().top,
        _bottom       = _top + $t.height(),
        compareTop    = partial === true ? _bottom : _top,
        compareBottom = partial === true ? _top : _bottom;

  return ((compareBottom <= viewBottom) && (compareTop >= viewTop));

};

})(jQuery);

但是，我想使用这段代码，以便检查它是否在可滚动元素。特别是我用于主要内容的主要标签。我将如何更改此代码以使其适用于我的可滚动元素？
我不太清楚该怎么做。我已经尝试将$ w变量更改为$（'main'），但这似乎表现得很奇怪。

However, I would like to use this piece of code so that it checks whether it is visible inside a scrollable element. Specifically the main tag which I used for my main content. How would I go about changing this code so that it works for my scrollable element? I'm not quite sure what to do. I've already tried changing $w variable to $('main') but that seems to behave odd.