Javascript: Loop Through every third child node

Question

If I got a parent node, how can I loop through every third child node?

I've got now this code:

var parents = document.getElementById('ID_of_parent');
var first_child = parents.firstChild.data.id;
alert(parents);
alert(first_child);

For the parents, i got now '[object HTMLDivElement]' and for first_child i got 'undefined'.

Answer 1

var nodes = document.getElementById('ID_of_parent').childNodes;
for(i=0; i<nodes.length; i+=3) {
    alert(nodes[i]);
}

Answer 2

Have you consider jQuery?

$("#ID_of_parent > *:nth-child(3n)").each(function() { alert(this);});

I implemented a demo here: http://jsbin.com/ahije4/5