TypeScript mode class Greeter { greeting: string; constructor (message: string) { this.greeting = message; } greet() { return "Hello, " + this.greeting; } } var greeter = new Greeter("world"); var button = document.createElement('button') button.innerText = "Say Hello" button.onclick = function() { alert(greeter.greet()) } document.body.appendChild(button) This is a specialization of the JavaScript mode.