如何从函数/实例外部访问变量

我有这个非常简单的JavaScript代码，它应该使用参数返回全名firstname和lastname当我在函数中提醒全名时，一切都可以正常工作。但是我正在努力如何使fullname变量从函数/实例外部访问？

这是我的代码：

var getName = function () {
    this.name = function (firstname, lastname, success) {
        var fullName = firstname + " " + lastname;
        success(fullName);
    };
};

var test = new getName();
test.name("John", "Smith", function (output) {
    var fullname = output;
    alert(fullname); //this works fine
    return fullname; // I need this variable to be accessed from outside this function
});
var myName = fullname; //I need to create the variable here
alert(myName); //this does not work

这是小提琴

非常感谢您的帮助。

编辑：我正在构建一个iPad应用程序，我正在使用cordova和javascript插件。其中一个插件使我可以访问设备中的文件。现在，我需要能够获取路径并在回调之外使用它，以便我可以在作用域中的任何位置使用：

这是插件代码：

var FileManager = function(){
this.get_path = function(todir,tofilename, success){
        fail = (typeof fail == 'undefined')? Log('FileManager','read file fail'): fail;
        this.load_file(
            todir,
            tofilename,
            function(fileEntry){
                var sPath = fileEntry.toURL();
                success(sPath);
            },
            Log('fail')
        );
    }

    this.load_file = function(dir, file, success, fail, dont_repeat){
        if(!dir || dir =='')
        {
            Log('error','msg')('No file should be created, without a folder, to prevent a mess');
            fail();
            return;
        }
        fail = (typeof fail == 'undefined')? Log('FileManager','load file fail'): fail;
        var full_file_path = dir+'/'+file;
        var object = this;
        // get fileSystem
        fileSystemSingleton.load(
            function(fs){
                var dont_repeat_inner = dont_repeat;
                // get file handler
                console.log(fs.root);
                fs.root.getFile(
                    full_file_path,
                    {create: true, exclusive: false},
                    success,
                    function(error){
                        if(dont_repeat == true){
                            Log('FileManager','error')('recurring error, gettingout of here!');
                            return;
                        }
                        // if target folder does not exist, create it
                        if(error.code == 3){
                            Log('FileManager','msg')('folder does not exist, creating it');
                            var a = new DirManager();
                            a.create_r(
                                dir,
                                function(){
                                    Log('FileManager','mesg')('trying to create the file again: '+file);
                                    object.load_file(dir,file,success,fail,true);
                                },
                                fail
                            );
                            return;
                        }
                        fail(error);
                    }
                );
            }
        );
    };
}

这是我如何使用它：

    var b = new FileManager(); // Initialize a File manager
    b.get_path('Documents','data.json',function(path){
        myPath = path;
        console.log(myPath); //this gives me the path of the file in the console, which works fine
        return myPath; //I return the path to be accessed outside
    });
    var filePath = myPath; //here I need to access the path variable
    console.log(filePath)// here, the path is undefined and it does not work
    //Since I'm using angular services to retrieve the data from json, I'd like to pass the filePath
  //this is a fraction of code for retrieving data:
  return $resource('data.json',{}, {'query': {method: 'GET', isArray: false}});
  //passing the value does not work
  return $resource(filePath,{}, {'query': {method: 'GET', isArray: false}});
  //even wrapping resource around instance does not work, it breaks the whole app
  b.get_path('Documents','data.json',function(path){
        myPath = path;
        console.log(myPath); //this gives me the path of the file in the console, which works fine
        return $resource(myPath,{}, {'query': {method: 'GET', isArray: false}});
    });

工厂服务：

'use strict';
angular
    .module ('myApp')
    .factory('getMeData', function ($resource) {
        var b = new FileManager(); // Initialize a File manager
        b.get_path('Documents','data.json',function(path){
            myPath = path;
            return myPath;
        });
        //below doesn't work when passing path (it is undefined)
        return $resource(myPath,{}, {'query': {method: 'GET', isArray: false}});
        //when wrapping it around, the app crashes
        b.get_path('Documents','data.json',function(path){
            myPath = path;
            return $resource(myPath,{}, {'query': {method: 'GET', isArray: false}});
        });
        //none of the solution above work
    });