function traverse(selector) {
    var node = document.querySelector(selector);

    if (node !== undefined && node !== null) {
        traverseNode(node, '');
    }

    function traverseNode(node, spacing) {

        spacing = spacing || '  ';

        var nodeId = node.getAttribute('id');
        var nodeClass = node.getAttribute('class');

        if (node.id) {
            console.log(info += ': id="' + node.id + '"');
        }

        if (node.className) {
            console.log(info += ': class="' + node.className + '"');
        }

        for (var i = 0; i < node.childNodes.length; i++) {
            var child = node.childNodes[i];
            if (child.nodeType === document.ELEMENT_NODE) {
                traverseNode(child, spacing + '  ');
            }
        }
    }
}

var selector = ".birds";
traverse(selector);