• 通过 getters/setters 来截取对对象成员的访问

class Person {
    private _age: number = 0;
    set age(val: number) {
        console.log('进入了set age方法');
        if (val < 0) {
            throw new Error('人的年龄不能小于零');
        }
        this._age = val;
    }

    get age(): number {
        console.log('进入了get age方法');
        return this._age;
    }
}

let p = new Person();
p.age = 18;

// 如下????代码本质类同：p.age(-6);
// p.age = -6;
console.log(p.age);