SO Question

http://stackoverflow.com/q/7382058/143739

HTML

<button id="b1">Button 1</button>
<button id="b2">Button 2</button>

JavaScript

var b1 = document.getElementById('b1'), b2 = document.getElementById('b2');
var x = "Hello!";
function showX() {
    alert(x);
}
b1.onclick = function() {
    document.write("yo");
    showX();
};
b2.onclick = function() {
    document.write("yoyo");
    showX();
};