Understanding and Implementing Design Patterns in TypeScript

Design Patterns are general solutions to recurring problems in software development. These patterns help to structure the code in an organized way, facilitating the maintenance, reuse and scalability of the system. In TypeScript, a superset of JavaScript, Design Patterns can be implemented even more efficiently due to strong typing and object-oriented features.

In this post, we will explore three main categories of Design Patterns (Creational, Structural, and Behavioral) and how to implement them in TypeScript.

1. Creational Patterns

Creational patterns deal with the creation of objects, helping to encapsulate the instance process and promote code reuse.

Example: Singleton

Singleton guarantees that a class has only a single instance throughout the entire application lifecycle.

class Singleton {
    private static instance: Singleton;

    private constructor() {}

    static getInstance(): Singleton {
        if (!Singleton.instance) {
            Singleton.instance = new Singleton();
        }
        return Singleton.instance;
    }

    someMethod() {
        console.log("Método do Singleton");
    }
}

const instance1 = Singleton.getInstance();
const instance2 = Singleton.getInstance();

console.log(instance1 === instance2); // true

In the example above, the getInstance() method ensures that only one instance of the Singleton class is created.

2. Structural Patterns

Structural patterns deal with the composition of classes and objects, ensuring that large code structures can be built from smaller, simpler pieces.

Example: Adapter

The Adapter pattern allows two incompatible interfaces to work together. This is useful when you want to use a class that has a different interface than what your code expects.

// Interface antiga
class OldAPI {
    oldRequest() {
        return "Dados da API antiga";
    }
}

// Interface nova
class NewAPI {
    newRequest() {
        return "Dados da API nova";
    }
}

// Adapter que adapta a interface antiga para a nova
class APIAdapter {
    private oldAPI: OldAPI;

    constructor(oldAPI: OldAPI) {
        this.oldAPI = oldAPI;
    }

    newRequest() {
        return this.oldAPI.oldRequest();
    }
}

const oldAPI = new OldAPI();
const adapter = new APIAdapter(oldAPI);

console.log(adapter.newRequest()); // "Dados da API antiga"

In this example, the Adapter (APIAdapter) allows the OldAPI class to be used with the interface expected by NewAPI.

3. Behavioral Patterns

Behavioral patterns deal with interaction and communication between objects, promoting flexibility and decoupling in code.

Example: Observer

The Observer pattern defines a one-to-many dependency between objects so that when an object changes state, all its dependents are notified and updated automatically.

interface Observer {
    update(data: any): void;
}

class Subject {
    private observers: Observer[] = [];

    addObserver(observer: Observer) {
        this.observers.push(observer);
    }

    removeObserver(observer: Observer) {
        this.observers = this.observers.filter(obs => obs !== observer);
    }

    notifyObservers(data: any) {
        this.observers.forEach(observer => observer.update(data));
    }
}

class ConcreteObserver implements Observer {
    update(data: any) {
        console.log("Observer atualizado com dados:", data);
    }
}

const subject = new Subject();
const observer1 = new ConcreteObserver();
const observer2 = new ConcreteObserver();

subject.addObserver(observer1);
subject.addObserver(observer2);

subject.notifyObservers("Alguma informação importante");
// Ambos observers recebem a atualização

In the example above, the Observer pattern allows multiple objects to observe and react to changes in the state of a subject object (Subject).

Conclusion

Design Patterns are powerful tools for building robust and scalable code. TypeScript, with its static typing and object-oriented characteristics, is an excellent environment to implement these standards, providing greater security and productivity in development.

By using creative, structural and behavioral patterns, you will be adopting practices that improve code readability and maintainability, ensuring effective solutions to common development problems.

I hope this post helped you understand how to apply Design Patterns in TypeScript. Try these implementations in your projects and see how they can improve the quality of your code!

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