Bootstrap 3 modal vertical position center

Question

This is a two part question:

1. How can you position the modal vertically in the center when you don\'t know the exact height of the modal?

2. Is

Answer 1

var modalVerticalCenterClass = ".modal";
function centerModals($element) {
    var $modals;
    if ($element.length) {
        $modals = $element;
    } else {
        $modals = $(modalVerticalCenterClass + ':visible');
    }
    $modals.each( function(i) {
        var $clone = $(this).clone().css('display', 'block').appendTo('body');
        var top = Math.round(($clone.height() - $clone.find('.modal-content').height()) / 2);
        top = top > 0 ? top : 0;
        $clone.remove();
        $(this).find('.modal-content').css("margin-top", top);
    });
}
$(modalVerticalCenterClass).on('show.bs.modal', function(e) {
    centerModals($(this));
});
$(window).on('resize', centerModals);