DOM2版

IE6とかじゃ動かないっぽい。

//NodeFilter. SHOW_ALL, SHOW_ENTITY_REFERENCE, SHOW_DOCUMENT_TYPE, SHOW_ELEMENT, SHOW_ENTITY, SHOW_FRAGMENT, SHOW_ATTRIBUTE, SHOW_PROCESSING_INSTRUCTION, SHOW_NOTATION, SHOW_TEXT, SHOW_COMMENT, SHOW_CDATA_SECTION, SHOW_DOCUMENT, 
var root = document.getElementsByTagName("body")[0];
var walker = document.createTreeWalker(root, NodeFilter.SHOW_ELEMENT, null, false);
while (walker.nextNode())
	console.log(walker.currentNode.nodeName)

ID特定のID(neko)のみ適用

function idFilter (node) {
	if (node.id == 'neko') {
		return NodeFilter.FILTER_ACCEPT;
	}	else {
		return NodeFilter.FILTER_SKIP;
	}
}
var root = document.getElementsByTagName("body")[0];
var walker = document.createTreeWalker(root, NodeFilter.SHOW_ELEMENT, idFilter, false);
while (walker.nextNode())
	console.log(walker.currentNode.nodeName);