OLOO how to access private variable

问题

In the following example I am using Kyle Simpson's "OLOO (Objects Linking to Other Objects) Pattern" to create a simple example of object serialization.

I need to keep variable _data private (I am using a closure) and expose its properties only with getter and setters which are create on object instance level (in init).

Currently I defined function toJson inside init so it can access _data and it works but, I would like to know:

• If would be possible to move toJson function outside init(place it at same level of fromJson) so it will accessible via protoype chain but allowing to access _data variable (I suspect it is not possible because _data it is in a closure).
• Otherwise could you suggest a better alternative(even using ES6) keeping in consideration that _data should not be enumerable and not modifiable apart using getter and setter?

        // example of serialization and deserialization of an object
        (function (window) {
            var dataApi = '{"id":0,"top":10,"left":20,"width":100,"height":150}';
            var state = JSON.parse(dataApi);
            var base = {
                init: function (data) {
                    var _data = data; // private
                    // defined on object itself not on its protoype
                    Object.defineProperty(this, 'id', {
                        get: function () {
                            return _data.id;
                        },
                        set: function (value) {
                            _data.id = value;
                        }
                    });
                    Object.defineProperty(this, 'top', {
                        get: function () {
                            return _data.top;
                        },
                        set: function (value) {
                            _data.top = value;
                        }
                    });
                    Object.defineProperty(this, 'left', {
                        get: function () {
                            return _data.left;
                        },
                        set: function (value) {
                            _data.left = value;
                        }
                    });
                    Object.defineProperty(this, 'width', {
                        get: function () {
                            return _data.width;
                        },
                        set: function (value) {
                            _data.width = value;
                        }
                    });
                    Object.defineProperty(this, 'height', {
                        get: function () {
                            return _data.height;
                        },
                        set: function (value) {
                            _data.height = value;
                        }
                    });
                    this.toJson = function () {
                        // move this function to prototype
                        return JSON.stringify(_data);
                    }
                },
                // defined on protoype
                fromJson: function (json) {
                    var data = JSON.parse(json),
                        obj = Object.create(this);
                    obj.init(data);
                    return obj;
                }
            };

            // create object with linked prototype using deserialization
            var wdgA = base.fromJson(dataApi);
            // serialize object
            var str = wdgA.toJson();
            console.log(str);

            // create object with data injection
            var wdgB = Object.create(base);
            wdgB.init(state);
            var id = wdgB.id;
            console.log(id);
        })(window);

回答1:

I need to keep variable _data private (I am using a closure). Would it be possible to move toJson function outside init?

No. Private variables cannot be accessed from outside.

来源：https://stackoverflow.com/questions/40395762/oloo-how-to-access-private-variable