To understand recursion, you must first understand recursion.

Recursion is a technique well suited to certain types of tasks. In this first lesson we’ll look at solving a problem that requires the flattening of arrays *without* using recursion. Showing the shortcoming of a non-recursive solution first will help you to understand why it’s so valuable and why sometimes it's the only solution to many problem.

Intro to Recursion - The Problem

In this lesson we manage to remove all of the nested loops that helped us towards a partial solution in the first lesson. We create a function `getTasks`, that can, only under certain conditions, call itself. This is the basis of recursion and often leads to cleaner, shorter code that can handle more dynamic input.

Intro to Recursion - The Solution

Our previous solution used `forEach` and a globally available array that could be mutated from inside our function. We can improve upon this and create a function that is easier to maintain & test by swapping our `forEach` loop for `reduce`. By removing the global array and instead making `getTasks` return a value directly we end up with a pure function.

Intro to Recursion - Refactoring to a Pure Function

When using recursion, you must be mindful of the dreaded `infinite loop`. Using the recursive function that we’ve built up over the previous lessons, we look at how a simple duplicated configuration item could cause chaos for our program as it has no context of which items it has previously seen. We fix this problem by introducing a `parents` array, which can keep track of which top-level commands have already been accessed.

...learn about recursion.

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