I finished it yesterday, got stuck for a while in the Asynchonous Callbacks exercise. It wasn't completely clear to me what you wanted.

I went back today and saw that you changed the exercise and description.

"Define a function named doStuffAsync that takes one argument callback, that reads the contents of the file "passwords", appends "OWNED" and writes the results to file "world.txt", then calls callback. Remember, read doesn't return the file contents directly."

From the description shown above, It wasn't clear that you wanted world.txt to contain the content of 'passwords' plus 'OWNED' appended.