jQuery Center in viewport method

jquery.centerInViewport.js

/**
 * Vertically center an element (popup modal) to the viewport
 * If the element is taller than the window height absolute positioning is
 * used so that the element will scroll with the docuemnt
 *
 * @param {boolean} animate             Animate to new position or move immediately? Defaults true
 * @param {boolean} centerHorizontal    Center the element horizontally? Defaults true
 * @param {boolean} centerVertical      Center the element vertically? Defaults true
 *
 * @chainable
 */
$.fn.centerInViewport = function (animate, centerHorizontal, centerVertical) {
    var POS_ABS = 'absolute',
        POS_FIX = 'fixed',
        $win = $(window),
        offset = this.offset(),
        docH = $('body').height();
        elH = this.height(),
        elW = this.width(),
        scrollTop = $win.scrollTop(),
        scrollLeft = $win.scrollLeft(),
        curLeft = offset.left - scrollLeft,
        curTop = offset.top - scrollTop,
        elBottom = offset.top + elH,
        winH = $win.height(),
        winW = $win.width(),
        posType = (this.css('position') === POS_FIX) ? POS_FIX : POS_ABS,
        newTop = (winH - elH) / 2,
        newLeft = Math.max((winW - elW) / 2, 0),
        animate = (animate !== false),
        centerHorizontal = (centerHorizontal !== false),
        centerVertical = (centerVertical !== false);

    // El height is greater that viewport height
    if (newTop < 0) {
        // Make sure the bottom of the element will fit on the page
        // otherwise shift it up til it does
        newTop = Math.min(docH - elBottom, 0);

        // Don't bother repositioning downwards
        if (newTop >= curTop) {
            centerVertical = false;
        }
        posType = POS_ABS;

        // Allow the element to scroll with the page
        this.css({
            position: POS_ABS,
            top: offset.top + 'px'
        });
    }

    if (!centerVertical) {
        newTop = curTop;
    }
    if (!centerHorizontal) {
        newLeft = curLeft;
    }
    
    if (posType === POS_ABS) {
        newTop += scrollTop;
        newLeft += scrollLeft;
    }

    if (animate) {
        this.animate({
            top: newTop,
            left: newLeft
        });
    } else {
        this.css({
            top: newTop + 'px',
            left: newLeft + 'px'
        });
    }
};