Mastering JavaScript Functional Programming - Second Edition

Recursion

Recursion is the most potent tool for developing algorithms and a great aid for solving large classes of problems. The idea is that a function can at a certain point call itself, and when that call is done, continue working with whatever result it has received. This is usually quite helpful for certain classes of problems or definitions. The most often quoted example is the factorial function (the factorial of n is written as n!) as defined for nonnegative integer values:

• If n is 0, then n!=1
• If n is greater than 0, then n! = n * (n-1)!

The value of n! is the number of ways that you can order n different elements in a row. For example, if you want to place five books in line, you can pick any of the five for the first place, and ...