What useful custom jQuery selectors have you written?

For me, one of the best, yet under-utilised feature of jQuery is the custom selector. I have a fairly trivial example of this, to pick out all text boxes that are empty:

$(document).ready(function() {
    $.extend($.expr[':'], {
        textboxEmpty: function(el) {
            var $el = $(el);
            return ($el.val() == "") &&开发者_Python百科 ($el.attr("type") == "text");
        }
    });
});

And to call:

alert($(":textboxEmpty").length);

I was wondering, really, if anyone else had some useful examples of custom selectors they have written.

I am, of course, not blind to the pitfalls of these, and realise that they can be quite slow and, as such, should be combined with other faster selectors. It would be useful to hear if there are any other problems we should be aware of.

I haven't written any, yet James Padolsey has a great collection of selector plug-ins (for elements in view, for external links, for elements with a specific .data property, etc)

If you are using ASP.NET, this selector will help you find server controls by id:

$.expr[":"].asp = function(a, i, m) {
    return $(a).attr('id') && $(a).attr('id').endsWith(m[3]);
};

If you had a server control that looked like

<asp:TextBox runat="server" ID="txtPhoneNumber" />

You could access it like this

$(":asp(txtPhoneNumber)")

EDIT

Forgot to add the endsWith extension

String.prototype.endsWith = function(str) {
    return (this.match(str + '$') == str);
};

As custom selectors are suggested on stackoverflow I'll add them here

Select 'URL' style

Selecting empty text input using jQuery