Inspired by Roger Johansson’s Levels of HTML Knowledge: alert("Hello World"); var WORLD = "World"; function hello(who) { alert("Hello " + who); }; hello(WORLD); <button onclick="hello(WORLD)">Say Hello</button> <button id="hello">Say Hello</button> var button = document.all.hello; button.onclick = function() { hello(WORLD); }; var button = document.getElementById("hello"); button.addEventListener(