Need to hook into a javascript function call, any way to do this?

Question

I'm trying to hook into a function that loads Facebook's news feed:

UIIntentionalStream.instance && UIIntentionalStream.instance.loadOlderPosts();

on Facebook.com.

Is there a way for me to do this with my own JavaScript? Basically, I need to have some sort of callback - when that function is called, I'd like my own function to be called.

Answer 1

A more complete method will be:

var old = UIIntentionalStream.instance.loadOlderPosts;
UIIntentionalStream.instance.loadOlderPosts = function(arguments) {
    // hook before call
    var ret = old.apply(this, arguments);
    // hook after call
    return ret;
};

This makes sure that if loadOlderPosts is expecting any parameters or using this, it will get the correct version of them as well as if the caller expects any return value it will get it