index.html

<script src="main.js"></script>

<button id='button1'>Click me</button>

main.js

window.addEventListener('DOMContentLoaded', function(event) {
	var appState = {
		buttonClicks: 0
	};

	function gavin(coffee) {
		if (coffee.type == "ButtonClick") {
			appState.buttonClicks++;
		}
	} 

	function drink() {
		window.requestAnimationFrame(drink);
		var button1 = document.getElementById("button1");

		if (appState.buttonClicks > 0) {
			button1.innerText = "You've clicked me " + appState.buttonClicks + " times!";
		}
	}

	var button1 = document.getElementById("button1");
	button1.addEventListener("click", function(event) {
		var babycino = {
			type: "ButtonClick"
		};
		gavin(babycino);
	})

	drink();
})