Pure Reducer Functions

Pure Reducer Functions Overview

At its core, pure reducer functions is about doing one thing well in Redux. Once you understand the pattern, you can apply it consistently across projects and teams.

Good pure reducer functions pays off across the whole project: fewer surprises, easier collaboration, and smoother onboarding. The snippet below is a solid starting point.

import { createSlice } from '@reduxjs/toolkit';

const counterSlice = createSlice({
  name: 'counter',
  initialState: { value: 0 },
  reducers: {
    increment: (state) => { state.value += 1; },
    addBy: (state, action) => { state.value += action.payload; },
  },
});

export const { increment, addBy } = counterSlice.actions;
export default counterSlice.reducer;

createSlice generates actions and a reducer together; Immer lets you write safe 'mutating' updates.

Pure Reducer Functions Example

const slice = createSlice({ name, initialState, reducers });
const store = configureStore({ reducer: { key: slice.reducer } });
// dispatch(slice.actions.something())

• Start from a minimal Pure Reducer Functions example and grow it only as needed.
• Keep things explicit so Pure Reducer Functions behaves the same for everyone on the team.
• Name things clearly so teammates understand your Pure Reducer Functions at a glance.
• Verify Pure Reducer Functions works as expected before relying on it in important work.

Redux Cheatsheet

Quick Redux Toolkit reference related to pure reducer functions.

How Pure Reducer Functions Works in Redux

Pure Reducer Functions follows Redux's predictable data flow: components dispatch actions, reducers compute the next state from the previous state and the action, and subscribed components re-render.

createSlice generates actions and a reducer together; Immer lets you write safe 'mutating' updates.

• State lives in a single, read-only store.
• Actions are the only way to describe a change.
• Reducers are pure functions that return the next state.
• Redux Toolkit removes most boilerplate with slices and thunks.

Practical Guidance for Pure Reducer Functions

In modern apps, pure reducer functions should use Redux Toolkit rather than hand-written Redux. Keep state minimal, colocate logic in slices, and use RTK Query for server data.

Common Mistakes

• Skipping edge cases and error handling when using pure reducer functions.
• Not verifying the result of pure reducer functions before moving on.
• Over-complicating pure reducer functions before you actually need the extra flexibility.
• Ignoring documentation, which makes pure reducer functions hard for the next person to follow.

Key Takeaways

• Pure Reducer Functions is a core part of working effectively with Redux.
• Start small and keep pure reducer functions focused on a single goal.
• Apply consistent patterns so pure reducer functions scales across your project.
• Practise and document pure reducer functions to keep your workflow maintainable.