Mastering JavaScript Functional Programming - Second Edition

Thinking recursively

The key to solving problems recursively is assuming that you already have a function that does whatever you need and just calling it normally. (Doesn't this sound weird? Actually, it is quite appropriate: if you want to solve a problem by using recursion, you must first have solved it before...) On the other hand, if you try to work out in your head how the recursive calls work and attempt to follow the flow in your mind, you'll probably just get lost. So what you need to do is the following:

1. Assume you already have an appropriate function to solve your problem.
2. See how the big problem can be solved by solving one (or more) smaller problems.
3. Solve those problems by using the imagined function from step 1.
4. Decide what ...