$.fn.do() method: Execute other code within a jQuery chain
I guess this plugin could be useful, however I think you can drop the async part since it's not any harder to call queue directly.

Also, I am not a huge fan of error swallowing or ignoring invalid calls since it makes the code harder to debug. If there's a call to do without providing a callback, you should let the developer be notified.

I also like to allow defining the this value for the callback function so that you do not need to use $.proxy for that purpose.

Finally I allowed to return a value from the callback to change the target object for the rest of the chain. However I am not so sure about this feature since it could harm code comprehension but I am leaving it there as an idea.

Basically it would be as simple as:

!function($) {
    $.fn.do = function (callback, thisArg) {
        if (typeof callback !== 'function') {
            throw new TypeError("the 'callback' argument must be of type 'function'");
        }

        return callback.call(thisArg || this, this) || this;
    };
}(jQuery);


Note: I've defined the plugin within an IIFE so that it still works if $.noConflict() was used.