trying to call javascript

There seems to be something BIG I am missing here? It would seem that I would need to tell the PHP program that register_extension() is a valid javascript function? 

Yes you are missing somthing big. You will have a hard time doing this if you don't start from the begining: learn how JavaScript works with plain HTML, how it interact with the browser and the server. Then, learn how to integrate your JavaScript code in a PHP application.

Thanks. This is the part I am currently missing:
>>Then, learn how to integrate your JavaScript code in a PHP application.

This is the part I am asking about.  Your comment reminds me of some comments I have seen about playing jazz guitar. They go like this: the person asks how do I add some jazz licks to my blues playing. The answer goes like this:

1) first learn all the notes on the neck
2) then learn all the scales
3) then learn all the chords in all the positions
4) then learn the arpeggios of all chords in 3 positions
5) learn to sight read

I know there are some guitar players up here who have seen this type of comment on the guitar websites. As a "functional" jazz guitarist I can tell you that it would take years and years to cover all that stuff. I have been playing for 45 years and know some of them, not all of them. Could I tell a newbie guitar player how to do it? No but I could point them in the right direction. I would tell them about "playing the changes". That is the crux of it. It is not the answer, but it is the "path" to success. I'd tell them about articles or books that cover that topic. 

If I am a little short, it is just that I am getting frustrated. Sorry. 

I am getting this response: Uncaught ReferenceError: register_extension is not defined

register_extension() calls my sendMessage(). If I could get past the CI interaction with JS, I am sure I could get the messaging working on my own. I am pretty good with a debugger.  

proof that an old dog can learn new tricks