Bootstrap 4 Stacked Modal

stacked_modal.js

$('.modal').on('show.bs.modal', function () {
    var $modal = $(this);
    var baseZIndex = 1050;
    var modalZIndex = baseZIndex + ($('.modal.show').length * 20);
    var backdropZIndex = modalZIndex - 10;
    $modal.css('z-index', modalZIndex).css('overflow', 'auto');
    $('.modal-backdrop.show:last').css('z-index', backdropZIndex);
});
$('.modal').on('shown.bs.modal', function () {
    var baseBackdropZIndex = 1040;
    $('.modal-backdrop.show').each(function (i) {
        $(this).css('z-index', baseBackdropZIndex + (i * 20));
    });
});
$('.modal').on('hide.bs.modal', function () {
    var $modal = $(this);
    $modal.css('z-index', '');
});