Returning content via jQuery without footers on admin pages

What you want to do is define a callback function to handle your request and to do that you need to hook onto:

wp_ajax_(action)

…where “(action)” is the name of your “action” parameter that needs to be supplied in your AJAX request (more on that in a moment).

First, define a callback function in your PHP logic, let’s use the example of unc_gallery_upload.

In this case, “unc_gallery_upload” is the name of your action, so when defining your hook, you combine wp_ajax_ with unc_gallery_upload, and you get wp_ajax_unc_gallery_upload, that’s the name of your action hook.

PHP

function unc_gallery_upload_handler() {
    //handle request e.g. var_dump($_POST['data']);
}

add_action( 'wp_ajax_unc_gallery_upload', 'unc_gallery_upload_handler' );

JavaScript

In your AJAX request (JS code)

var options = {
    //this will post to example.com/wp-admin/admin-ajax.php
    //the ajaxurl variable is already defined in the global
    //scope of the WordPress dashboard
    url: ajaxurl,
   //your payload, accessible on $_POST['data']
    data: {
        //this name of your action as defined in your wp_ajax_(action)
        //hook that will fire your
        action: 'unc_gallery_upload',
        payload: 'somedata'
    },
    target: '#targetLayer',
    beforeSubmit: beforeSubmit,
    uploadProgress: uploadProgress,
    resetForm: true,
    complete: complete
};

$('#uploadForm').submit(function() {
    $(this).ajaxSubmit(options);
    return false;
});

I strongly recommend reading: wp_ajax_(action)

Note: since you are in the admin the area, you do NOT want to define a wp_ajax_nopriv_(action).