Strategy Pattern

Information drawn from

• Medium - Javascript design patterns

It is a behavioural design pattern that allows encapsulation of alternative algorithms for a particular task. It defines a family of algorithms and encapsulates them in such a way that they are interchangeable at runtime without client interference or knowledge.

In the example below, we create a class Commute for encapsulating all the possible strategies for commuting to work. Then, we define three strategies namely Bus, PersonalCar, and Taxi. Using this pattern we can swap the implementation to use for the travel method of the Commute object at runtime.

// encapsulation
class Commute {
  travel(transport) {
    return transport.travelTime();
  }
}

class Vehicle {
  travelTime() {
    return this._timeTaken;
  }
}

// strategy 1
class Bus extends Vehicle {
  constructor() {
    super();
    this._timeTaken = 10;
  }
}

// strategy 2
class Taxi extends Vehicle {
  constructor() {
    super();
    this._timeTaken = 5;
  }
}

// strategy 3
class PersonalCar extends Vehicle {
  constructor() {
    super();
    this._timeTaken = 3;
  }
}

// usage
const commute = new Commute();

console.log(commute.travel(new Taxi())); // 5
console.log(commute.travel(new Bus())); // 10

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Last update on 04 Feb 2020

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