anatomy of GDownloadUrl

I am using GDownloadUrl to send client data to server.here the sode I used

GDownloadU开发者_StackOverflow中文版rl(
        dwnld_url,
        function(data) {
            if(!empty(data)){

                // Parsing XML
                var xml_doc = GXml.parse(data);

            } else {

                alert ('Could not genarate the Attractions. Please try again!');
            }
        },
        tmp_xml_doc
);

can you please explain me what this function(data) means.I read the documentation.but confused.can you suggest me good tutrial for this because I am new to web programming.thanks in advance

The function(data) {...} is an anonymous function. This function is called when the response of the dnwnld_url is returned. The function is called with the response data and it is up to you to handle the data in the body of the anonymous function. Now you parse it to xml so you can do something with the xml result.

Hope this made some sense for you.

Cheers!