class property in typescript

gistfile1.txt

class Greeter {
    greeting: string;
    constructor(message: string) {
        this.greeting = message;
    }
    greet = () => {
        return "Hello, " + this.greeting;
    }
    // greet() {
    //     return "Hello, " + this.greeting;
    // }
}

let greeter = new Greeter('world');

let foo = {
    bar: greeter.greet
}

let button = document.createElement('button');
button.textContent = "Say Hello";
button.onclick = function() {
    alert(foo.bar());
}

document.body.appendChild(button);