编辑“︁JavaScript面向对象设计模式”︁（章节）

== 行为型模式 ==
行为型模式关注对象间的通信和职责分配。

=== 观察者模式（Observer Pattern） ===
定义对象间的一对多依赖关系，当一个对象状态改变时，所有依赖者自动收到通知。

<syntaxhighlight lang="javascript">
class Subject {
  constructor() {
    this.observers = [];
  }

  subscribe(observer) {
    this.observers.push(observer);
  }

  unsubscribe(observer) {
    this.observers = this.observers.filter(obs => obs !== observer);
  }

  notify(data) {
    this.observers.forEach(observer => observer.update(data));
  }
}

class Observer {
  update(data) {
    console.log(`Received data: ${data}`);
  }
}

const subject = new Subject();
const observer1 = new Observer();
const observer2 = new Observer();

subject.subscribe(observer1);
subject.subscribe(observer2);
subject.notify('Hello World!');
// 输出:
// Received data: Hello World!
// Received data: Hello World!
</syntaxhighlight>

=== 策略模式（Strategy Pattern） ===
定义一系列算法，封装每个算法，并使它们可以互换。

<syntaxhighlight lang="javascript">
class PaymentStrategy {
  pay(amount) {}
}

class CreditCardStrategy extends PaymentStrategy {
  pay(amount) {
    console.log(`Paid ${amount} via Credit Card`);
  }
}

class PayPalStrategy extends PaymentStrategy {
  pay(amount) {
    console.log(`Paid ${amount} via PayPal`);
  }
}

class ShoppingCart {
  constructor() {
    this.strategy = null;
  }

  setStrategy(strategy) {
    this.strategy = strategy;
  }

  checkout(amount) {
    this.strategy.pay(amount);
  }
}

const cart = new ShoppingCart();
cart.setStrategy(new CreditCardStrategy());
cart.checkout(100); // 输出: Paid 100 via Credit Card
</syntaxhighlight>