单一职责原则

单一职责原则（Single Responsibility Principle,SRP）

核心思想：一个类只负责一个功能领域中的相应职责

案例分析：

案例一：

1、实现动物类，拥有跑方法，符合单一职责

class Animal {
  constructor(name) {
    this.name = name
  }
  running() {
    console.log(`${this.name} is running`)
  }
}
const dog = new Animal('dog')
dog.running()
const cat = new Animal('cat')
cat.running()

2、添加需求，拥有游泳方法

• 方法一

  class Animal {
    constructor(name, type) {
      this.name = name
      this.type = type
    }
    running() {
      if (this.type == '陆生') {
        console.log(`${this.name} is running`)
      }
      if (this.type == '水生') {
        console.log(`${this.name} is swimming`)
      }
    }
  }
  const dog = new Animal('dog', '陆生')
  dog.running()
  const fish = new Animal('fish', '水生')
  fish.running()
  

  违背单一职责原则，running方法需要区分水生还是陆生，添加别的类型时也需要修改running方法。

• 方法二

  class Animal {
    constructor(name) {
      this.name = name
    }
    running() {
      console.log(`${this.name} is running`)
    }
    swimming() {
      console.log(`${this.name} is swimming`)
    }
  }
  const dog = new Animal('dog')
  dog.running()
  const fish = new Animal('fish')
  fish.swimming()
  

  方法符合单一职责原则，区分了running和swimming，但类不符合单一职责原则。容易出现狗调用swimming的情况。

• 方法三

  class TerrestrialAnimal {
    constructor(name) {
      this.name = name
    }
    running() {
      console.log(`${this.name} is running`)
    }
  }
  class AquaticAnimal {
    constructor(name) {
      this.name = name
    }
    swimming() {
      console.log(`${this.name} is swimming`)
    }
  }
  const dog = new TerrestrialAnimal('dog')
  dog.running()
  const fish = new AquaticAnimal('fish')
  fish.swimming()
  

  根据职责将动物拆分成陆生生物和水生生物，符合单一职责原则。

案例二：

有一个UserManager类，它负责用户验证、用户数据存储以及向用户发送通知，这违反了单一职责原则。

interface User {
  username: string;
  email: string;
}
​
class UserManager {
  validateUser(user: User): boolean {
      // 用户验证逻辑
      return true; // 假设验证总是成功
  }
​
  storeUser(user: User): void {
      // 用户存储逻辑
      console.log(`${user.username} stored in database.`);
  }
​
  sendNotification(user: User, message: string): void {
      // 发送通知逻辑
      console.log(`Notification sent to ${user.username}: ${message}`);
  }
​
  createUser(user: User): void {
      if (!this.validateUser(user)) {
          console.log('User validation failed.');
          return;
      }
      this.storeUser(user);
      this.sendNotification(user, 'User created successfully.');
  }
}

将UserManager类的职责拆分为三个类：UserValidator、UserStorage、和UserNotifier，每个类只负责一个功能。

interface User {
    username: string;
    email: string;
}
​
class UserValidator {
    validate(user: User): boolean {
        // 用户验证逻辑
        return true; // 假设验证总是成功
    }
}
​
class UserStorage {
    store(user: User): void {
        // 用户存储逻辑
        console.log(`${user.username} stored in database.`);
    }
}
​
class UserNotifier {
    send(user: User, message: string): void {
        // 发送通知逻辑
        console.log(`Notification sent to ${user.username}: ${message}`);
    }
}
​
class UserManager {
    private validator = new UserValidator();
    private storage = new UserStorage();
    private notifier = new UserNotifier();
​
    createUser(user: User): void {
        if (!this.validator.validate(user)) {
            console.log('User validation failed.');
            return;
        }
        this.storage.store(user);
        this.notifier.send(user, 'User created successfully.');
    }
}

参考：learn.lianglianglee.com/%e4%b8%93%e…