Preloader on file upload

Meanwhile found out CKEDITOR.editor.dialogShow

CKEDITOR.instances

> Object {post-textarea: a}

CKEDITOR.instances['post-textarea'].dialogShow(function(e) { console.log(e.evt, e.data); });

> TypeError: undefined is not a function

am I missing something? 

Meanwhile the only alternative I have is playing around with the DOM... (disclaimer: this code is kind of ridiculous)

function createPreloader() {
    setTimeout(function(){ // any callback after this dialog is loaded!?
        $('.cke_dialog_ui_fileButton').click(function(){ 
            var filePath = $(this).parent().parent().parent().find('iframe').contents().find('input[type="file"]').val());
            if (filePath != '') {
                // it's uploading, sweet!
                $(this).insertAfter('<div class="ck-file-loader">Loading, please wait...</div>');
            }
        });
    }, 500);
}

// needs a callback refering to ckeditor after-initialization
$('.cke_button__image').click(createPreloader);
$('.cke_button__video').click(createPreloader);