class Greeter {
    greeting: string;

    constructor(message: string) {
        this.greeting = message;
    }
    greet(): string {
        return this.greeting;
    }
};

let greeter = new Greeter("Hello, world!");
console.log(greeter.greet());

Here we have a class, Greeter, that has a constructor and a greet method. We can construct an instance of the class using the new keyword and pass in a string we want the greet method to output to the console. The instance of our Greeter class is stored in the greeter variable which we then us to call the greet method.