# 工厂模式

## 定义

定义一个创建对象的接口，但让实现这个接口的类来决定实例化哪个类。

工厂方法让类的实例化推迟到子类中进行。

## 场景

### 优点 

隐藏原始类，方便之后的代码迁移

### 缺点

多了层封装，会造成类的数目过多，系统复杂度增加。

## JavaScript实现

```javascript
/**
 * 实体类：Dog、Cat
 */

class Dog {
  run() {
    console.log("狗");
  }
}

class Cat {
  run() {
    console.log("猫");
  }
}

/**
 * 工厂类：Animal
 */

class Animal {
  constructor(name) {
    name = name.toLocaleLowerCase();
    switch (name) {
      case "dog":
        return new Dog();
      case "cat":
        return new Cat();
      default:
        throw TypeError("class name wrong");
    }
  }
}

/**
 * 以下是测试代码
 */

const cat = new Animal("cat");
cat.run();
const dog = new Animal("dog");
dog.run();
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mm.ricky.moe/other/she-ji-mo-shi-1/gong-chang-mo-shi.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.