任务链模式 js

class Handler {
  constructor(nextHandler = null) {
    this.nextHandler = nextHandler;
  }

  setNext(handler) {
    this.nextHandler = handler;
    return handler;
  }

  handle(request) {
    if (this.nextHandler) {
      return this.nextHandler.handle(request);
    }
    return null;
  }
}

class ConcreteHandlerA extends Handler {
  handle(request) {
    if (request === 'A') {
      return `ConcreteHandlerA handled ${request}`;
    } else {
      return super.handle(request);
    }
  }
}

class ConcreteHandlerB extends Handler {
  handle(request) {
    if (request === 'B') {
      return `ConcreteHandlerB handled ${request}`;
    } else {
      return super.handle(request);
    }
  }
}

// 使用示例
const handlerA = new ConcreteHandlerA();
const handlerB = new ConcreteHandlerB();
handlerA.setNext(handlerB);

console.log(handlerA.handle('A')); // ConcreteHandlerA handled A
console.log(handlerA.handle('B')); // ConcreteHandlerB handled B
console.log(handlerA.handle('C')); // null