javascript 对象之间的关系处理

function UserEntity() {
        var userName = null;

        var userProtoType = (function() {
            var inside = false;
            return {
                "userName": {
                    get: function() {
                        return userName;
                    },
                    set: function(value) {
                        //设置条件，如果是没有满足设置的条件，则不允许set
                        if (!inside) {
                            return false;
                        }
                        userName = value;
                    }
                },
                setUserName: {
                    value: function(value) {
                        inside = true;
                        this.userName = value;
                        inside = false;
                    },
                    writable: false, // 只读
                    configurable: false // 不可配置
                }
            }
        })();

        Object.defineProperties(this, userProtoType);
    }

    UserEntity.prototype.setUserName = function(value) {
        this.userName = value;
    }
    var arc = new UserEntity();
    arc.userName = '张三' //外部设置
    console.log(arc.userName);//输出：null
    arc.setUserName('李四');//内部设置
    console.log(arc.userName);//输出：李四