Understanding Crockford's walk_the_dom (“The Good Parts”)

Question

I'm trying to work through to understand Crockford's walk_the_dom function below. Here is my logic and the DOM tree I am working with. I don't see when node.nextSibling is reached.

function walk(node, func) {
    func(node);
    node = node.firstChild;
    while (node) {
        walk(node, func);
        node = node.nextSibling;
    }
};

1. func(node) runs a function on the given node.
2. node=node.firstChild() is now equal to the firstChild of document.body, or in this case, H1
3. while(node) runs a loop where the walk function is run again.
4. func(node) now runs a function on H1
5. node = node.firstChild() is now equal to the firstChild of H1 , also known as #text in this case
6. while(node) runs a loop where the walk function is run again

7. func(node) runs a function on #text

8. node = node.firstChild() --> what is the firstChild of #text ?

9. when is node.nextSibling reached?

Answer 1

The firstChild of #text is null or undefined because there isn't any. JavaScript has what is known as truthy values. So while(null) is the same as while(false) .