Retrieving External Content into Lithium Component

here is my code working with some JSON Web services.

function callAjax() {
    LITHIUM.jQuery.ajax({
        url: "${ajaxURL}",
        dataType: 'jsonp',
        jsonp: 'callback',
        jsonpCallback: 'callbackFunctionOnceJsonpReturnedProperly',
        timeout: ${ajaxTimeout},
        success: function(){
            //alert("success");
        },
        error: function (jqXHR, textStatus, errorThrown) {
            .......
        }
    });
}

function callbackFunctionOnceJsonpReturnedProperly(data, textStatus, xhr){
    if (typeof (data) == 'undefined' || data == null) {
        alert("jsonpCallback object is null");
        return;
    }
    
    var username = data["username"];      
}