Chain of responsibility pattern

Information drawn from

• Medium - Javascript design patterns by Soumyajit Pathak

This is a behavioural design pattern that provides a chain of loosely coupled objects. Each of these objects can choose to act on or handle the request of the client.

A good example of the chain of responsibility pattern is the event bubbling in DOM in which an event propagates through a series of nested DOM elements, one of which may have an “event listener” attached to listen to and act on the event.

In this example, we create a class CumulativeSum, which can be instantiated with an optional initialValue. It has a method add that adds the passed value to the sum attribute of the object and returns the object itself to allow chaining of add method calls.

class CumulativeSum {
  constructor(intialValue = 0) {
    this.sum = intialValue;
  }

  add(value) {
    this.sum += value;
    return this;
  }
}

// usage
const sum1 = new CumulativeSum();
console.log(sum1.add(10).add(2).add(50).sum); // 62


const sum2 = new CumulativeSum(10);
console.log(sum2.add(10).add(20).add(5).sum); // 45

This is a common pattern that can be seen in jQuery as well, where almost any method call on a jQuery object returns a jQuery object so that method calls can be chained together.

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Last update on 20 Feb 2020

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