Upload file on creating new event

You can see that the form submission is intercepted and sent using a special $.post() request:

$("#f").submit(function () {
    var f = $("#f");
    $.post(f.attr("action"), f.serialize(), function (result) {
        close(eval(result));
    });
    return false;
});

You'll have to use FormData and $.ajax() in order to submit the data including the file.

See also:
https://stackoverflow.com/questions/21214608/jquery-ajax-single-file-upload

You might need to play with this snippet a little bit - as far as I can see the accepted answer uses this:

var fd = new FormData($("#fileinfo"));

which needs to be replaced with

var fd = new FormData($("#fileinfo")[0]);