React Native By Example

Changes are made with pure functions

The idea of a pure function comes from functional programming, and can be summarized as follows:

• Given the same arguments, a pure function always returns the same result
• Regardless of our application state, a pure function is able to execute
• Variables outside of a pure function's scope cannot be modified by it

These three principles correlate with three major parts of the Redux ecosystem: actions, reducers, and store.

Actions are how we can indirectly modify our read-only state. Reducers are the pure functions that perform that modification. The single store in Redux is where our state exists.