Question

I’m using jQuery $.getJSON(..) to get some json.

The passed value shows me “undefined”.

Is there a way to do that?

getTopMenuJson : function(currentPage) {
    if(currentPage == null) currentPage = 1;

    var retJSON;

    $.getJSON(
            requestURLs.topMenuJson, 
            {
                'ITEM_PER_PAGE' : TopMenuHandler.ITEM_PER_PAGE,
                'CURRENT_PAGE' : currentPage
            },
            function(JSON) {
                //alert(JSON); **<--This gives me result (Object)**
                retJSON = JSON;
            }
    );

    **alert(retJSON); //<!-- This doesn't, but Undefined**
},

Answer 1

It doesn’t and it shouldn’t as getJSON is internally doing an AJAX call, the first A in AJAX stands for Asynchronous, it simply means that the script execution won’t wait until your success function is called.

You could instead use $.ajax and pass in async: false to one of its options to make sure that your script waits for the ajax call to be finished, but be aware that doing that would freeze the browser / tab until your AJAX call is finished.

$.ajax({
  url: requestURLs.topMenuJson,
  dataType: 'json',
  data:  
  {
     'ITEM_PER_PAGE' : TopMenuHandler.ITEM_PER_PAGE,
     'CURRENT_PAGE' : currentPage
  },
  success: function(JSON) {
     //alert(JSON); **<--This gives me result (Object)**
     // this won't work without async:false
     // as the execution of script won't wait until this function 
     // is finished
     retJSON = JSON; 
  },
  async: false
});

http://api.jquery.com/jQuery.ajax/

async Default: true By default, all requests are sent
asynchronously (i.e. this is set to true by default). If you need
synchronous requests, set this option to false. Cross-domain requests
and dataType: “jsonp” requests do not support synchronous operation.
Note that synchronous requests may temporarily lock the browser,
disabling any actions while the request is active.