Strategy Pattern

Name: Strategy Pattern
Rating: 1.3 (3065 reviews)
Author: francescoxx

Algorithm Encapsulation

GitHub Link: https://github.com/FrancescoXX/Design-Patterns-Strategy-Javascript

Behavioral Design Pattern

Intro

The Strategy pattern, also called policy pattern, enables selecting an algorithm at runtime.
Deferring the decision about which algorithm to use, allows more flexibility and reusability

⚡️Recognize

When we want to change the behavior of our application at runtime

For example, change the behavior to:

aggressive
defensive
balanced

💡Intent

Define different algorithms
Make them interchangeable at runtime, with a setStrategy() method

🔧 Apply when

Classes only change in behavior
We want Different variants of an algorithm

✅Pro

Algorithm families use inheritance for common parts Avoid conditional statements using this pattern Clients can choose the required behavior

⚠️Cons

Increased number of objects
Strategies are shared between objects

🏆 Great for

Encapsulate an algorithm
Change algorithm at runtime

/**
 * STRATEGY PATTERN JAVASCRIPT IMPLEMENTATION
 */

//Concrete Strategy A
class AggressiveStrategy {
    constructor() {
        this.next = move => "Next aggressive move";
    }
}

//Concrete Strategy B
class BalancedStrategy {
    constructor() {
        this.next = move => "Next balanced move";
    }
}

//Concrete Strategy C
class DefensiveStrategy {
    constructor() {
        this.next = move => "Next defensive move";
    }
}

//Strategy
class AIGameStrategy {
    constructor() {
        this.setStrategy = (game) => this.game = game;
        this.next = move => this.game.next(move);
    }
}

// --- MAIN ---

//Strategies initialization
const aggressive = new AggressiveStrategy();
const balanced = new BalancedStrategy();
const defensive = new DefensiveStrategy();

//Implement Strategy Pattern
const AI = new AIGameStrategy();

//Set Defensive Strategy
AI.setStrategy(defensive);

//Perform defensive action
console.log(AI.next()); //Next defensive move

//Set Balanced Strategy...
AI.setStrategy(balanced);

//Perform balanced actions
console.log(AI.next()); //Next balanced move
console.log(AI.next()); //Next balanced move
console.log(AI.next()); //Next balanced move

//Change Strategy to Aggressive
AI.setStrategy(aggressive);

//Perform aggressive actions
console.log(AI.next()); //Next aggressive move
console.log(AI.next()); //Next aggressive move

GitHub Link: https://github.com/FrancescoXX/Design-Patterns-Strategy-Javascript