Question

Here is the contents of get.json:

{ “id” : 1, “name” : “hello” }

and the script/markup:

var entries = [];

       function Data(){}
       Data.prototype.get = function(id){
            var object = {}, length = entries.length, success = false;
            for (var i = 0; i < length; i++) {
                if (entries[i].id == id) {
                    object = entries[i];
                    i = length;
                    console.log("From browser: " + object.name);
                    success = true;
                }
            }
            if (!success) {
                $.getJSON("get.json", function(data){
                    entries.push(data);
                    object = data;
                    console.log("Newly fetched: " + object.name);
                });
            }
            return object;
        }

        $(function(){
            var data = new Data();
            data.get(1);
            console.log((data.get(1).name);
        });

Answer 1

I would use a callback. If the data exists in the browser cache, the callback will be fired immediately. If not, it will be fired when the Asynchronous request finishes.

function Data(){}
Data.prototype.get = function(id, callback){
     var object = {}, length = entries.length, false;
     for (var i = 0; i < length; i++) {
         if (entries[i].id == id) {
             object = entries[i];
             console.log("From browser: " + object.name);
             callback(object);
             return; // Don't let execution continue
         }
     }

     $.getJSON("get.json", function(data){
         entries.push(data);
         object = data;
         console.log("Newly fetched: " + object.name);
         callback(object);
     });
 }

 $(function(){
     var data = new Data();
     data.get(1, function(obj){
        console.log(obj.name);
     });
 });

Another way would to be to make your AJAX call synchronous which would pause all execution, but that is a very bad idea.

Edit: I also changed your code a little to remove the success variable, and chose to return right from the for loop (thereby breaking the loop).