Javascript: Save AJAX Result in as Class variable

I know that javascript does not use Class, at least not in common sense`. I will like to know how to return and save an AJAX return value in a class variable rather than calling multiple methods within the callback.

var Reader = function(){
  //Initialize some variables
  this.data = null;
}

Reader.prototype.makeAjaxCall = function(urlPath){
   //Make and Ajax call and return some value
   Ajax.success(function(data){
     this.data = data;
   });
}

Reader.prototype.searchData = function(param){
   //Needs access to this.data
}
Reader.prototype.findData = function(id){
  //Needs access to this.data
}

Reader.prototype.deleteItem = function(id){
  // Needs access to this.data
}

In the above code, whatever function that needs access to the data property needs to be called within the ajax success callback, so If I have ten methods that need data, I will have to line all of them up within the callback, which I do not feel is right. How do I minimise the number of functions in the callback and ensure in some other ways that the function is successful and data is saved the instance variable data.