javascript / jQuery中的回调函数参数

Question

Trying to go through a book to learn jQuery ui. I run into this code

 $("#autocomplete").autocomplete({
     minLength: 2,
     source: function (request, response) {
         $.getJSON("https//api.github.com/search/repositories", {
             q: request.term + " in:name"
         })
             .then(function (data) {
             var matches = $.map(data.items, function (repo) {
                 return repo.full_name;
             });
             response(matches);
         });
     }
 });

In the .then(function(data){}), is the data object passed by the result of $.getJSON() function? I checked jQuery API. I think in this case I am dealing with doneFilter callback but the API didn't mention any default object that is passed in the function. Can anyone explain more about this behavior? And why the data object contains a items property?

Answer 1

You are dealing with a promise object. As of jQuery 1.5, all of jQuery's Ajax methods return a superset of the XMLHTTPRequest object. This jQuery XHR object, or "jqXHR," returned by $.getJSON() implements the Promise interface, giving it all the properties, methods, and behavior of a Promise.

so .then() will get called after the completion of async call and it will use the success response object in data as an input.

FOR MORE DETAILS ON PROMISE

http://davidwalsh.name/write-javascript-promises