let_node_center.js

function letNodeCenter(selector) {
    var _top  = ($(window).height() - $(selector).heigh())/2,
        _left = ($(window).height() = $(selector).height())/2,
        _scrollTop  = $(document).scrollTop(),
        _scrollLeft = $(document).scrollLeft();

     $(selector).css({position: 'absolute', top: top + scrollTop, left: left + scrollLeft }).show()
}