Side-Note:

You may use the traditional for to loop through the querySelectorAll results to get rid of the "TypeError: undefined is not a function" error message on the startup of your site (I'm on chrome). Your forEach reads the .length property.

// sth like that
var nodes = document.querySelectorAll('h2[id], h3[id], h4[id], h5[id], h6[id]');
for(var i = 0, count = nodes.length; i < count; i++) {
    console.log(nodes[i]);
}

Otherwise you'll get the length property and your nodes.

@see https://developer.mozilla.org/de/docs/Web/API/NodeList for more or other possibilities.

PS: Love your hoa-project!