getXpath.js

function XPath(elm) {
       for (segs = []; elm && elm.nodeType == 1; elm = elm.parentNode) {
         if (elm.hasAttribute('id')) {
           segs.unshift('id("' + elm.getAttribute('id') + '")')
           return segs.join('/')
         }
         else if (elm.hasAttribute('class'))
           segs.unshift(elm.localName.toLowerCase() + '[@class="' + elm.getAttribute('class') + '"]')
         else {
           for (i = 1, sib = elm.previousSibling; sib; sib = sib.previousSibling)
             if (sib.localName == elm.localName) i++
           segs.unshift(elm.localName.toLowerCase() + '[' + i + ']')
         }
       }
       return segs.length ? '/' + segs.join('/') : null
}

<!-- 方法2 -->
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;
}


//Gets an XPath for an node

var getNodeXPath = function(node) {
    if (node && node.id)
        return '//*[@id="' + node.id + '"]';
    else
        return getNodeTreeXPath(node);
};

var getNodeTreeXPath = function(node) {
    var paths = [];

    // Use nodeName (instead of localName) so namespace prefix is included (if any).
    for (; node && (node.nodeType == 1 || node.nodeType == 3) ; node = node.parentNode)  {
        var index = 0;
        // EXTRA TEST FOR ELEMENT.ID
        if (node && node.id) {
            paths.splice(0, 0, '/*[@id="' + node.id + '"]');
            break;
        }

        for (var sibling = node.previousSibling; sibling; sibling = sibling.previousSibling) {
            // Ignore document type declaration.
            if (sibling.nodeType == Node.DOCUMENT_TYPE_NODE)
                continue;

            if (sibling.nodeName == node.nodeName)
                ++index;
        }

        var tagName = (node.nodeType == 1 ? node.nodeName.toLowerCase() : "text()");
        var pathIndex = (index ? "[" + (index+1) + "]" : "");
        paths.splice(0, 0, tagName + pathIndex);
    }

    return paths.length ? "/" + paths.join("/") : null;
};

还有一个jquery的官方插件：jquery.ellocate.js 提供该功能。