document.getElementByID("test").innerHTML giving TypeError: 'undefined' is not a function (evaluating 'document.getElementByID("test")')

It's document.getElementById and not document.getElementByID.

You can test this right now using firebug or chrome dev tools on this site by doing:

document.getElementById('hlogo').innerHTML='It works!'; // have a look at the logo

JavaScript is case sensitive. Watch your capitalization closely when you write JavaScript statements:

A function getElementById is not the same as getElementbyID.

A variable named myVariable is not the same as MyVariable.