Reselect

Reselect Overview

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

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

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

const selectItems = (state) => state.cart.items;

export const selectCartTotal = createSelector(
  [selectItems],
  (items) => items.reduce((sum, i) => sum + i.price * i.qty, 0),
);

createSelector memoizes derived data so it only recomputes when its inputs change.

Reselect Example

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

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

Redux Cheatsheet

Quick Redux Toolkit reference related to reselect.

How Reselect Works in Redux

Reselect 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.

createSelector memoizes derived data so it only recomputes when its inputs change.

• 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 Reselect

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

Key Takeaways

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