链接原型和原型继承

Question

function Person(name){
    this.name=name
}
var julia=new Person("Julia");

Person.prototype.sayName=function(){
return "Hello, dear "+ this.name;
}

function Other(name){
this.name=name;
}

var mike=new Other("Mike");

Other.prototype=Object.create(Person.prototype);
mike.sayName();

When I call mike.sayName(); it doesn't work and I get mike.sayName is not a function. I dont understand why? By using Object.create I let Other.prototype inherit from the Person prototype which had the method sayName. Now, why am I not being able to run mike.sayName();

Thanks!!!

Answer 1

The prototype property of a constructor is only special because it's used as the [[Prototype]] value when creating instances. However, replacing prototype with another object will only affect instances created after the change, it won't magically update the [[Prototype]] of existing instances.

var oldproto = Other.prototype;
var mike = new Other("Mike");
Object.getPrototypeOf(mike); // oldproto
Other.prototype = Object.create(Person.prototype);
Object.getPrototypeOf(mike); // oldproto

So just swap the order:

Other.prototype = Object.create(Person.prototype);
var mike = new Other("Mike");