Redux Reducers

Reducers Overview

Reducers lets you work with Redux in a way that stays clear, repeatable, and easy to scale. Instead of ad-hoc steps, you follow a pattern that other developers recognise immediately.

The key is to keep reducers focused and predictable. Start from the minimal example here, then add only the complexity your situation actually needs.

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.

Reducers Example

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

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

Redux Cheatsheet

Quick Redux Toolkit reference related to reducers.

How Reducers Works in Redux

Reducers 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 Reducers

In modern apps, reducers 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

• Copying reducers commands or snippets without understanding what each part does.
• Skipping edge cases and error handling when using reducers.
• Not verifying the result of reducers before moving on.
• Over-complicating reducers before you actually need the extra flexibility.

Key Takeaways

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