get children of a parent element by tag names

getChildrenByTags.js

/*!
 * get children of a parent element by tag nameS
 * gist.github.com/englishextra/d4789c5d30f6f6b429fdf7aaebeda7b1
 * based on quirksmode.org/dom/getElementsByTagNames.html
 * takes two arguments:
 * A string with a comma-separated list of tag names.
 * An optional start element, otherwise document is used.
 * var element = document.getElementById('test');
 * var formFieldList = getElementsByTagNames('input,select,textarea',element);
 */
function getChildrenByTags(list, obj) {
	if (!obj) {
		var obj = document;
	}
	var tagNames = list.split(",");
	var resultArray = new Array();
	for (var i = 0; i < tagNames.length; i++) {
		var tags = obj.getElementsByTagName(tagNames[i]);
		for (var j = 0; j < tags.length; j++) {
			resultArray.push(tags[j]);
		}
	}
	var testNode = resultArray[0];
	if (!testNode) {
		return [];
	}
	if (testNode.sourceIndex) {
		resultArray.sort(function (a, b) {
			return a.sourceIndex - b.sourceIndex;
		});
	} else if (testNode.compareDocumentPosition) {
		resultArray.sort(function (a, b) {
			return 3 - (a.compareDocumentPosition(b) & 6);
		});
	}
	return resultArray;
}