blah.js

function getData() {
  $.ajax({
    url: "blah.html",
    success: function(data) {
      var data1 = data;
      $.ajax({
        url: "blah2.html",
        success: function(data) {
          console.log("callback hell");
        },
        error: function(data) {
         ... 
        }
      });
    },
    error: function(data) {
      // retry
      $.ajax({
        url: "blah.html",
        success: function(data) {
          // do something
        },
        error: function(data) {
          ...
        }
      });
    }
  });
  return data1;
}