How to calculate the XPath position of an element using Javascript?

Firebug can do this, and it's open source (BSD) so you can reuse their implementation, which does not require any libraries.

3rd party edit

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Xpath.getElementXPath = function(element){    if (element && element.id)        return '//*[@id="' + element.id + '"]';    else        return Xpath.getElementTreeXPath(element);};

Above code calls this function.Attention i added some line-wrapping to avoid horizontal scroll bar

Xpath.getElementTreeXPath = function(element){    var paths = [];  // Use nodeName (instead of localName)     // so namespace prefix is included (if any).    for (; element && element.nodeType == Node.ELEMENT_NODE;            element = element.parentNode)    {        var index = 0;        var hasFollowingSiblings = false;        for (var sibling = element.previousSibling; sibling;               sibling = sibling.previousSibling)        {            // Ignore document type declaration.            if (sibling.nodeType == Node.DOCUMENT_TYPE_NODE)                continue;            if (sibling.nodeName == element.nodeName)                ++index;        }        for (var sibling = element.nextSibling;             sibling && !hasFollowingSiblings;            sibling = sibling.nextSibling)        {            if (sibling.nodeName == element.nodeName)                hasFollowingSiblings = true;        }        var tagName = (element.prefix ? element.prefix + ":" : "")                           + element.localName;        var pathIndex = (index || hasFollowingSiblings ? "["                    + (index + 1) + "]" : "");        paths.splice(0, 0, tagName + pathIndex);    }    return paths.length ? "/" + paths.join("/") : null;};

A function I use to get an XPath similar to your situation, it uses jQuery:

function getXPath( element ){    var xpath = '';    for ( ; element && element.nodeType == 1; element = element.parentNode )    {        var id = $(element.parentNode).children(element.tagName).index(element) + 1;        id > 1 ? (id = '[' + id + ']') : (id = '');        xpath = '/' + element.tagName.toLowerCase() + id + xpath;    }    return xpath;}

Small, powerfull and pure-js function

It returns xpath for the element and elements iterator for xpath.

https://gist.github.com/iimos/e9e96f036a3c174d0bf4

function xpath(el) {  if (typeof el == "string") return document.evaluate(el, document, null, 0, null)  if (!el || el.nodeType != 1) return ''  if (el.id) return "//*[@id='" + el.id + "']"  var sames = [].filter.call(el.parentNode.children, function (x) { return x.tagName == el.tagName })  return xpath(el.parentNode) + '/' + el.tagName.toLowerCase() + (sames.length > 1 ? '['+([].indexOf.call(sames, el)+1)+']' : '')}

Probably you will need to add a shim for IE8 that don't support the [].filter method: this MDN page gives such code.

Usage

var xp = xpath(elementNode)

var iterator = xpath("//h2")var el = iterator.iterateNext();while (el) {  // work with element  el = iterator.iterateNext();}