Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

// Getters and setters
class Temperature {
    private _celsius: number;

constructor(celsius: number) {
        this._celsius = celsius;
    }

get celsius(): number { return this._celsius; }
    set celsius(value: number) {
        if (value < -273.15) throw new RangeError("Below absolute zero");
        this._celsius = value;
    }

get fahrenheit(): number { return this._celsius * 9 / 5 + 32; }
    set fahrenheit(value: number) { this.celsius = (value - 32) * 5 / 9; }

get kelvin(): number { return this._celsius + 273.15; }
}

const t = new Temperature(100);
console.log(t.fahrenheit); // 212
t.fahrenheit = 32;
console.log(t.celsius);    // 0

// Singleton pattern with private constructor
class AppConfig {
    private static instance: AppConfig | null = null;

private constructor(
        public readonly apiUrl: string,
        public readonly debug: boolean,
    ) {}

static getInstance(): AppConfig {
        if (!AppConfig.instance) {
            AppConfig.instance = new AppConfig(
                process.env["API_URL"] ?? "https://api.example.com",
                process.env["NODE_ENV"] !== "production",
            );
        }
        return AppConfig.instance;
    }
}

const cfg1 = AppConfig.getInstance();
const cfg2 = AppConfig.getInstance();
console.log(cfg1 === cfg2); // true — same instance