Chain of Responsibility

Idea: Allow multiple objects to handle a request - each “handler” will either take an action based on the request or forward it to the next in the chain. This allows a sender to make a request without explicitly knowing which object should receive/handle it (or .

Connection: Error handling, algebraic effects (untyped), CLOS condition system

abstract class Handler {
  successor?: Handler
  abstract handleRequest(request: string): void;
}

class HandlerA extends Handler {
  handleRequest(request) {
    if (request === "A") {
      console.log("A handled");
    } else if (this.successor) {
      this.successor.handleRequest(request);
    } else {
      console.log(`Error: ${request} not handled!`);
    }
  }
}

class HandlerB extends Handler {
  handleRequest(request) {
    if (request === "B") {
      console.log("B handled");
    } else if (this.successor) {
      this.successor.handleRequest(request);
    } else {
      console.log(`Error: ${request} not handled!`);
    }
  }
}

function main() {
  const handlerA = new HandlerA();
  handlerA.successor = new HandlerB();
  handlerA.handleRequest("B"); // "B handled"
}