Array.map can mutate original array

https://dev.to/lofiandcode/can-map-mutate-the-original-array-yes-dmb

TL;DR:

Things to consider when using .map():

• Write your callback function carefully because it can modify the original array.
• In your callback function, always create new objects for every object in the original array. Otherwise you will just be copying pointers to the original objects.