varbook={};Object.defineProperties(book,{_year:{value:2004},edition:{value:1},year:{get:function(){returnthis._year;},set:function(newValue){if(newValue>2004){this._year=newValue;this.edition+=newValue-2004;}}}});vardescriptor=Object.getOwnPropertyDescriptor(book,"_year");alert(descriptor.value);//2004alert(descriptor.configurable);//falsealert(typeofdescriptor.get);//"undefined"vardescriptor=Object.getOwnPropertyDescriptor(book,"year");alert(descriptor.value);//undefinedalert(descriptor.enumerable);//falsealert(typeofdescriptor.get);//"function"以下这两行看不懂alert(descriptor.configurable);//falsealert(descriptor.enumerable);//false对象默认的可配置属性和可枚举属性是true吧示例代码未设置这两个属性，默认的应该为true吧PS：红宝书6.1.3（24印143页）