The whole point of the state is to take an existing state, apply an action to it, and produce a new state. It can be written like this:
old state + action = new state
Imagine, if you were performing basic calculations, then you would start writing it like this:
// sum is 0let sum = 0;// sum is now 3sum +=3;
The Redux way of doing things, though, is to change the preceding to:
let sum = 0;let sumWith3 = sum + 3;let sumWith6 = sumWith3 + 3;
We don't mutate anything but rather produce a new state for everything we do. Let's look at different constructs and what it means in practice to not mutate.
