prototype 为何是不能被打印显示的呢? 那么它的意义是什么? function Person(name, age) { this.name = name; this.age = age; } Person.prototype.sayHello = function() { console.log(`Hello, my name is ${this.name} and I'm ${this.age} years old.`); } let person1 = new Person('John', 30); person1.sayHello(); // 可调用 console.log(person1); // 没有原型上被定义的数据 console.log(person1.prototype); // undefined