Filling a SharePoint web service gap: Fetching current username, using client-side only jQuery Ajax

I'm stumped as for why no such service was included in the first place, seeing as the code is a one-liner, and I imagine it quite useful to most service clients.

Having first settled on a custom service (code here) to deliver the user name, deploying that isn't always an option. If you've only got client-side access to the portal, you *need* to do it with a script..

So I came up with this solution, which should work in most cases:

window.userInfo = 
{
    /* Public interface */
    getCurrentUsername: function(callback)
    {
        $.get(
            "/_layouts/userdisp.aspx?Force=True", 
            null, 
            function(data)
            {
                var username = window.userInfo._findUsernameFieldText(data);
                callback(username);
            }, "html");
    },
    
    /* Private interface */
    _findUsernameFieldText: function(pageData)
    {
        var fields = $(pageData).find("table.ms-formtable td#SPFieldText");
        for(var i = 0; i < fields.length; ++i)
        {
            field = fields.get(i);
            for(node = field.firstChild; 
                node.nextSibling != null; 
                node = node.nextSibling)
            {
                if(node.nodeType == 8 && /FieldInternalName=\"UserName\"/.test(node.nodeValue))
                    return $(field).text().replace(/(^[\s\xA0]+|[\s\xA0]+$)/g, '');
            }
        }
        return null;
    }
};

What I realized, as I pondered this yesterday, is that there are obviously a lot of pages in the portal which lists the current user's info - including the user profile page. Extracting the username should be no harder than asynchronously loading the page (using jQuery) and parsing the resulting form looking for a field commented with 'FieldInternalName="UserName"'.

Should the userdisp page be violently customized, this would be less likely to work, but being a _layouts page; such a customization is unlikely.

Granted the above code, you can test it by pasting that (in a script tag) plus the following into the html source of a content editor web part:

<script src="http://www.google.com/jsapi"></script>
<script type="text/javascript">
    google.load("jquery", "1");
    google.setOnLoadCallback(function() 
    {
        userInfo.getCurrentUsername(function(usr) { alert("[" + usr + "]"); });
    });
</script>

Full source code download here.