Setup jQuery AJAX & show errors

ajax_setup.js

/**
 * Setup jQuery AJAX
 *
 * Requires noty.js and 2 its layouts: noty/layouts/top.js, noty/layouts/topRight.js
 */
$.ajaxSetup({
    error: function(xhr, status, error) {
        // we ignore aborted XHR or when user press F5 while XHR is in progress
        if (status == 'abort' || xhr.readyState == 0)
            return;

        // default error message
        var text = 'Sorry, but request has failed';
        if (error)
            text += ' (' + error + ')';

        if (xhr.responseText) {
            text = xhr.responseText;

            if (text.toLowerCase().indexOf('</html>') != -1) {
                // HTML error message will be displayed in <iframe>
                var msg = noty({type: 'error', layout: 'top'});
                var iframe = $('<iframe>').appendTo(msg.$message.find('.noty_text'));

                var doc = iframe.contents()[0];
                doc.open();
                doc.write(text);
                doc.close();

                var width = msg.$message.width();
                iframe.width(width);

                var height = Math.min($(doc).find('body').outerHeight(true), $(document).height());
                iframe.height(height);
            } else if (text.length > 2000) {
                // large error message > 2000 symbols
                noty({type: 'error', layout: 'top', text: text});
            } else {
                noty({type: 'error', layout: 'topRight', text: text});
            }
        } else {
            noty({type: 'error', layout: 'topRight', text: text});
        }
    },

    /**
     * Handles error and info messages from backend. Example JSON:
     *
     *     {data: 'message', type: 'error', text: 'An error has occurred'}
     */
    success: function(response, status, xhr) {
        if (response && response.data == 'message') {
            noty({
                'type': response.type,
                'text': response.text
            });
        }
    }
});