Redux Explained in Depth

Source: Dev.to

Introduction

State management is one of the hardest problems in front‑end development. As applications grow, keeping data consistent across components becomes complex, error‑prone, and difficult to debug. Redux was created to solve this problem with a strict, predictable architecture.

Redux is a predictable state container for JavaScript applications. It is most commonly used with React, but it is framework‑agnostic and can work with Angular, Vue, Svelte, or vanilla JavaScript. Redux does not manage UI; it manages application state in a centralized, structured, and predictable way.

Problems Redux Solves

• Prop drilling (passing data deeply through components)
• Multiple sources of truth
• Unclear state mutation
• Difficult debugging
• Inconsistent UI behavior

As apps scale, state becomes shared, mutable, and hard to trace. Redux enforces rules that eliminate these problems.

Core Principles

1. Single source of truth – The entire application state lives in one JavaScript object called the store.
2. Read‑only state – The state cannot be modified directly; the only way to change it is by dispatching an action.
3. Pure reducers – State changes are handled by reducers, which are pure functions.

These principles lead to benefits such as easy debugging, centralized data, time‑travel debugging, and state persistence.

Building Blocks

Redux consists of five core building blocks:

• Store
• State
• Actions
• Reducers
• Middleware

Store

The store is the heart of Redux. It holds the entire state tree, provides access to the state, and allows updates via dispatch. It also registers listeners.

import { createStore } from 'redux';

const store = createStore(reducer);

The store exposes three methods:

• store.getState() – returns the current state
• store.dispatch(action) – sends an action to the reducer
• store.subscribe(listener) – registers a listener for state changes

State

State is a plain JavaScript object. Example:

{
  user: {
    id: 1,
    name: "Alex"
  },
  cart: {
    items: [],
    total: 0
  }
}

Important rules:

• State is immutable.
• State is serializable.
• The shape of the state should be intentional and explicit.

Actions

An action is a plain object that describes what happened.

{
  type: "ADD_TODO",
  payload: "Learn Redux"
}

Rules for actions:

• Must have a type property.
• Must be serializable.
• Should describe events, not contain logic.

Action creator example:

function addTodo(text) {
  return {
    type: "ADD_TODO",
    payload: text
  };
}

Reducers

Reducers are pure functions that calculate the next state based on the previous state and an action.

function todoReducer(state = [], action) {
  switch (action.type) {
    case "ADD_TODO":
      return [...state, action.payload];
    default:
      return state;
  }
}

Rules for reducers:

• Never mutate the state.
• No async code or side effects.
• Always return a new state (or the unchanged state).

Large apps split reducers by domain using combineReducers:

import { combineReducers } from 'redux';

const rootReducer = combineReducers({
  user: userReducer,
  cart: cartReducer
});

Middleware

Middleware extends Redux with custom behavior between dispatch and the reducer. Common use cases include logging, async requests, error handling, and analytics.

Redux itself is synchronous. To handle async logic, the thunk middleware allows dispatching functions:

store.dispatch((dispatch) => {
  fetchData().then(data => {
    dispatch({ type: "SUCCESS", payload: data });
  });
});

Typical flow with middleware:

1. Action dispatched.
2. Middleware intercepts.
3. Async work (if any) happens.
4. Real action dispatched.
5. Reducer calculates new state.

One‑Way Data Flow

Redux enforces a strict one‑way data flow:

UI → Action → Middleware (optional) → Reducer → Store → UI

This predictability eliminates hidden mutations, bidirectional data flow, and implicit state changes. Every state change can be logged, replayed, debugged, and tested.

When to Use Redux

Redux is not required for every application. Consider it when:

• State is shared widely across many components.
• State logic is complex.
• Debugging and traceability are important.
• The app is large or expected to grow.

Avoid Redux for small apps with mostly local state and simple updates.

Redux Toolkit (RTK)

Today, Redux Toolkit is the recommended way to work with Redux. It reduces boilerplate, uses Immer internally for immutable updates, enforces best practices, and includes useful middleware by default.

Example of creating a slice with RTK:

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

const counterSlice = createSlice({
  name: "counter",
  initialState: 0,
  reducers: {
    increment: state => state + 1
  }
});

RTK keeps Redux powerful without the usual complexity.

Common Misconceptions

• ❌ Redux is only for React – Redux is a state architecture, not a UI tool, and works with any front‑end framework or plain JavaScript.
• ✔ Redux is not a UI library – It does not render components; it only manages state.

Conclusion

Redux is a state‑management philosophy that enforces discipline, predictability, explicit data flow, and long‑term maintainability. When used correctly, it scales better than most alternatives and provides reliable, debuggable, and scalable state management for complex applications.