xpath.js

// path needs tail tweaks

var tagname = function (node) {
    return node.tagName || "#text";
};

var xpath = function (node, idx, tag, path) {
    idx = idx || 0;
    tag = tag || tagname(node);
    path = path || "";
    var left = node.previousSibling;
    var parent = node.parentNode;
    // console.log(node, node.nodeType, idx, tag, path);
    if (node.nodeType === 9) { // #document, root
        return path;
    } if (left) {
        if (tagname(left) === tag) { idx = idx + 1;}
        return xpath(left, idx, tag, path);
    } else if (parent) {
        path = "/" + tag + "[" + idx + "]" + path;
        return xpath(parent, 0, null, path);
    }
};

// xpath(document.getSelection().focusNode)
// "/HTML[0]/BODY[0]/DIV[0]/DIV[0]/DIV[1]/DIV[1]/DIV[2]/DIV[0]/DIV[6]/DIV[0]/DIV[0]/P[0]/SPAN[0]/#text[1]"
// xpath(document.getSelection().anchorNode)
// "/HTML[0]/BODY[0]/DIV[0]/DIV[0]/DIV[1]/DIV[1]/DIV[2]/DIV[0]/DIV[6]/DIV[0]/DIV[0]/P[0]/SPAN[0]/#text[1]"