TypeScript Classes and Object-Oriented Programming

Basic Class

class Person {
    name: string;
    private age: number;

    constructor(name: string, age: number) {
        this.name = name;
        this.age = age;
    }

    greet(): string {
        return `Hi, I am ${this.name}`;
    }

    getAge(): number {
        return this.age;
    }
}

const alice = new Person("Alice", 25);
console.log(alice.greet());    // Hi, I am Alice
console.log(alice.getAge());   // 25

Constructor Shorthand

class Point {
    constructor(
        public x: number,
        public y: number,
        private label: string = "point"
    ) {}

    toString(): string {
        return `${this.label}(${this.x}, ${this.y})`;
    }
}

const p = new Point(3, 4);
console.log(p.toString());  // point(3, 4)

Inheritance

class Animal {
    constructor(public name: string) {}
    speak(): string { return "..."; }
}

class Dog extends Animal {
    constructor(name: string, public breed: string) {
        super(name);
    }
    speak(): string { return `${this.name} barks!`; }
}

const rex = new Dog("Rex", "Labrador");
console.log(rex.speak());  // Rex barks!

Implementing Interfaces

interface Serializable {
    toJSON(): string;
    fromJSON(json: string): void;
}

class Config implements Serializable {
    private data: Record = {};

    toJSON(): string {
        return JSON.stringify(this.data);
    }
    fromJSON(json: string): void {
        this.data = JSON.parse(json);
    }
}

Abstract Classes

abstract class Shape {
    abstract area(): number;
    describe(): string {
        return `This shape has area ${this.area().toFixed(2)}`;
    }
}

class Circle extends Shape {
    constructor(private radius: number) { super(); }
    area(): number { return Math.PI * this.radius ** 2; }
}

const c = new Circle(5);
console.log(c.describe());  // This shape has area 78.54