CODESAMPLE

Chain of Responsibility - JavaScript

Chain of Responsibility JavaScript

The Chain of Responsibility pattern promotes decoupling the sender of a request from its receivers by passing the request along a chain of handlers. Each handler decides either to process the request or to pass it to the next handler in the chain. This allows for a flexible system where handlers can be added or removed without affecting the others.

The JavaScript implementation uses objects as handlers, each with a handle method and a next property pointing to the next handler. The handle method checks if it can process the request; if not, it delegates to next. The initial request is passed to the first handler in the chain. This approach leverages JavaScript’s flexible object model and prototypal inheritance (though not explicitly used here, it’s a common functional pattern). It avoids tight coupling and promotes a more modular design.

// Handler interface (implicitly defined through structure)

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

  setNext(handler) {
    this.next = handler;
    return handler; // For chaining setNext calls
  }

  handle(request) {
    if (this.next) {
      return this.next.handle(request);
    }
    return null; // Request not handled
  }
}

// Concrete Handlers

class ConcreteHandler1 extends Handler {
  handle(request) {
    if (request.type === "type1") {
      console.log("ConcreteHandler1 handling request:", request);
      return "Handler 1 processed the request";
    }
    return super.handle(request);
  }
}

class ConcreteHandler2 extends Handler {
  handle(request) {
    if (request.type === "type2") {
      console.log("ConcreteHandler2 handling request:", request);
      return "Handler 2 processed the request";
    }
    return super.handle(request);
  }
}

class ConcreteHandler3 extends Handler {
  handle(request) {
    if (request.type === "type3") {
      console.log("ConcreteHandler3 handling request:", request);
      return "Handler 3 processed the request";
    }
    return super.handle(request);
  }
}

// Client code

const handler1 = new ConcreteHandler1();
const handler2 = new ConcreteHandler2();
const handler3 = new ConcreteHandler3();

handler1.setNext(handler2).setNext(handler3);

const requests = [
  { type: "type1", data: "data1" },
  { type: "type2", data: "data2" },
  { type: "type3", data: "data3" },
  { type: "type4", data: "data4" } // Not handled
];

requests.forEach(request => {
  const result = handler1.handle(request);
  if(result) {
    console.log("Result:", result);
  } else {
    console.log("Request not handled.");
  }
});