js 属性类型

        var book = {
            _year: 2004,
            edition: 1
        };
        Object.defineProperty(book, "year", {
            get: function () {
                return this._year;
            },
            set: function (newValue) {
                if (newValue > 2004) {
                    this._year = newValue;
                    this.edition += newValue - 2004;
                }
            }
        });
        book.year = 2005;
        alert(book.edition);//2

        var book = {};
        Object.defineProperties(book, {
            _year: {
                value: 2004
            },
            edition: {
                value: 1
            },
            year: {
                get: function () {
                    return this._year;
                },
                set: function (newValue) {
                    if (newValue > 2004) {
                        this._year = newValue;
                        this.edition += newValue - 2004;
                    }
                }
            }
        });