Question

我是学习JavaScript概念的新手。想了解原型继承是如何工作的。我的印象是，如果你的类继承了它的父类，并且你在两个类的原型中有相同的命名方法，当你在子实例上调用方法时，将调用子原型中的方法。

代码：

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

Animal.prototype.printName = function () {
    console.log(this.name + ' in animal prototype');
}

function Cat(name) {
    Animal.call(this, name);
}



Cat.prototype.printName = function () {
    console.log(this.name + ' in cat prototype');
}

Cat.prototype = Object.create(Animal.prototype);

var anm1 = new Animal('mr cupcake');
anm1.printName();


var cat1 = new Cat('cat');
cat1.printName();

在调用cat1.printName（）时，我希望它能记录'cat in cat prototype'，但它记录了'cat in Animal prototype'。有人可以向我解释一下原因。感谢。

Answer 1

您是对的，但重置printName()时，您对Cat.prototype函数的覆盖本身会被下一行覆盖。只需移动代码的顺序即可解决问题：

＆＃13;

function Animal(name) {
   this.name = name;
}

Animal.prototype.printName = function() {
  console.log(this.name + ' in animal prototype');
}

function Cat(name) {
   Animal.call(this, name);
}

// OLD LOCATION of code

// This was overriding your override!
// Setting the prototype of an object to another object
// is the basis for JavaScript's prototypical inhertiance
// This line replaces the existing prototype object (which is
// where your override was) with a completely new object.
Cat.prototype = Object.create(Animal.prototype);

// NEW LOCATION
// AFTER setting the prototype (and creating inheritance),
// it is safe to do the override:
Cat.prototype.printName = function() {
  console.log(this.name + ' in cat prototype');
}

var anm1 = new Animal('mr cupcake');
anm1.printName();  // "mr cupcake in animal prototype" 

var cat1 = new Cat('cat');
cat1.printName();   // "cat in cat prototype"

＆＃13;

JavaScript原型覆盖

1 个答案: