Basic Browserify example

I've been banging my head against the wall for a while now, trying to get browserify working for me. I'm starting with what should be really the simplest example, replacing a javascript page with its browserified page (when there's no requires in it!). So, here's what I did:

I had a page, "javascript.js" that was already incorporated into my site. I went to its folder, and ran the command

browserify ./javascript.js > bundle.js

I figure that should be an identical file (functionally) to javascript.js. So, I go to my index.jade file and replace

script(src='javascript.js')

with

script(src='bundle.js')

(Those are the equivalent of script tags in html)

But it didn't work! The website now throws the error that a certain variable from my browserified file is undefined (the error comes from a function call in another file). What gives? What am I doing wrong? Am I thinking about bundles incorrectly? It seems like this is following instructions, but it's just not working.

Thanks for the help in advanced, I've really been at this for a while now with no progress.