对象属性设置器
定义对象，多属性 defineProperties
访问器属性 数据属性
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Object.defineProperties(book, {
_year: {
value: 2004
},
edition: {
value: 1,
writable: true
},
year: {
get: function() {
return this._year;
},
set: function(newValue) {
if (newValue > 2004) {
this._year = newValue;
this.edition += newValue - 2004;
}
}
}
});
book.edition = 2;
console.log(book.edition)
获取对象属性特性 getOwnPropertyDescriptor