Difference between dataType jsonp and JSON

Question

I download Jquery UI autoload, looking to remote-jsonp.html. This is ajax function but i open console.. I can't see any request in my console...

What is difference between dataType;"jsonp" and dataType;"JSON"

$( "#city" ).autocomplete({
        source: function( request, response ) {
            $.ajax({
                url: "http://ws.geonames.org/searchJSON",
                dataType: "jsonp",
                data: {
                    featureClass: "P",
                    style: "full",
                    maxRows: 12,
                    name_startsWith: request.term
                },
                success: function( data ) {
                    response( $.map( data.geonames, function( item ) {
                        return {
                            label: item.name + (item.adminName1 ? ", " + item.adminName1 : "") + ", " + item.countryName,
                            value: item.name
                        }
                    }));
                }
            });
        },

Reference http://jqueryui.com/demos/autocomplete/remote-jsonp.html

Answer 1

dataType: jsonp for cross-domain request, that means request to different domain and dataType: json for same domain-same origin request.

Loads in a JSON block using JSONP. Adds an extra "?callback=?" to the end of your URL to specify the callback. Disables caching by appending a query string parameter, "_=[TIMESTAMP]", to the URL unless the cache option is set to true.

Read about same origin policy

Read more about jQuery AJAX

Answer 2

With JSONP you shouldn't see an ajax request if that's what you're looking for. You should however see a request for the resource because JSONP is used for cross domain calls to pull in data from different domains.

It returns your JSON data wrapped in a function name. jQuery handles the function name behind the scenes and passes the data into your success handler. The data is loaded by dynamically creating a script element with the src attribute pointing to the service being called and then attached to the browser's DOM. Then the browser makes a request to the resource and the web service responds with the callback function and data.