[jQuery] How to extend a function

[jQuery] How to extend a function


Hi,
I'm using thickbox to show content around a site, but the core
thickbox.js is shared by multiple sites. For one particular site, I
need to add some custom javascript when certain thickbox functions are
called, such as TB_show and TB_remove.
I've tried the code below, but this doesn't work.
TB_show.extend({
    $(".mpu").css("visibility","hidden");
})
Any idea how I can extend an existing function?