$('a.modalButton').on('click', function(e) {
    var src = $(this).attr('data-src');
    var height = $(this).attr('data-height') || 300;
    var width = $(this).attr('data-width') || 400;
    
    $("#myModal iframe").attr({'src':src,
                        'height': height,
                        'width': width});
});

$('a.btn').on('click', function(e) {
    var src = $(this).attr('data-src');
    var height = $(this).attr('data-height') || 300;
    var width = $(this).attr('data-width') || 400;
    
    $("#myModal iframe").attr({'src':src,
                        'height': height,
                        'width': width});
});

Update modal.js