[jQuery] creating own callback

[Eric Teubert]

Hi,

I spend some time in browsing through the documentation but I didn't
find anything about creating own functions with callback-
functionality. How do I do this?

What I want to do:
Write a function that preloads an image and returns a callback when
the image is loaded. It looks like

jQuery.extend({
        preloadImage: function(imagePath) {
        jQuery("<img>").attr("src", "gfx/"+imagePath);
        }
});

$.preloadImage("example.gif");

But how have I to edit the first part when I want the second to look
like the following?

$.preloadImage("example.gif", function() { alert("Preloading
finished"); });

Thanks!