How to create a store using pure functions

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Pure functions produce the same output value, given the same input. They have no side-effects, and are easier to read, understand and test.

Given all this, I would like to create a store that hides the state but at the same time uses pure functions.

Immutability

Pure functions don’t modify their input. They treat the input values as immutable.

An immutable value is a value that, once created, cannot be changed.

Immutable.js provides immutable data structures like List. An immutable data structure will create a new data structure at each action.

Consider the next code:

import { List } from "immutable";
const list = List();
const newList = list.push(1);

push() creates a new list that has the new element. It doesn’t modify the existing list.

delete() returns a new List where the element at the specified index was removed.

The List data structure offers a nice interface for working with lists in an immutable way, so I will use it as the state value.

The Store

The store manages state.