var allDivsinDom = document.getElementsByTagName('div'); //Array of all divs
    var allAnchorinDom = document.getElementsByTagName('a'); //Array of all a
....

function readHTML(node) {
    var i, child;
    if (node.nodeType == 1) { // only tags
        for (i = 0 ; i < node.childNodes.length ; ++i) {
            child = node.childNodes[i];
            // do something with node
            window.console.info(child.tagName);
            readHTML(child);
        }
    }
}
readHTML(document.body);