Why can't my javascript code in the head selection get an element?

Question

I have been working on a pi calculator in javascript for a long time now and I have finally finished. The problem is that my script in the head section:

document         


        

Answer 1

Wrap it on a window onload event:

window.onload = function()
{
    document.getElementById("button").addEventListener('click', (function(){
        alert('Beginning…');
    }), false);
};

or

window.addEventListener('load', function()
{
    document.getElementById("button").addEventListener('click', (function(){
        alert('Beginning…');
    }), false);
});

or, if your script doesn't have to be in the head, put it after the element that has the id of button.

DEMO