class的访问器成员

• 本质是 class 的语法糖 等价于对象的defineProperty
• 对象里面也能使用

class Product{
            constructor(count, price){
                this.count = count;
                this.price = price;
            }
            get total(){ // 相当于getter
                return this.count * this.price;
            }
        }
 const product = new Product(10, 100);
 console.log(product.total); // 1000
 product.count = 20;
 console.log(product.total); // 2000

const product = {
            price: 100,
            count: 10,
            get total() { // 相当于getter
                return this.price * this.count;
            },
            set total(value) { 
            // 相当于setter 改变时会影响price的值.
       			 this.price = value / this.count; 
    		},
	};
console.log(product.total); // 1000
product.count = 20;
console.log(product.total); // 2000