JQuery deferred
var ajax_request = function(data){
return $.ajax(url,{
data: data,
dataType: "json",
method: "POST"
});
};
var req1 = ajax_request({})
.fail(function(jqXHR, textStatus, errorThrown){});
var req2 = ajax_request({})
.fail(function(jqXHR, textStatus, errorThrown){});
$.when(req1,req2).done(function(datareq1,datareq2){
//...
});