Mastering Redux: Essential Concepts and Best Practices for React Developers

Application Scenarios

As JavaScript single‑page applications become more complex, managing constantly changing state becomes difficult.

Redux was created to solve state‑related data problems.

In React, data flows in one direction within components.

Because data flows from parent to child via props, communication between sibling components is cumbersome.

Design Philosophy

Redux stores the entire application state in a single place called the store.

The store contains a state tree.

Components dispatch actions to the store instead of directly notifying other components.

Other components subscribe to the store’s state to refresh their views.

Three Core Principles

The whole application state is stored in a single object tree that lives in one unique store.

State is read‑only; the only way to change state is by dispatching an action, which is a plain object describing an event, processed by pure reducer functions.

A single source of truth makes component communication easier and enables unified state management.

Store

The store is the container where all data is kept; there should be only one store in an application. Redux provides a createStore function to generate the store.

The createStore function takes a reducer as an argument and returns a new Store object.

State

The store holds all data. A snapshot of the store at a specific moment is called the State, which can be retrieved via store.getState().

Redux dictates that one State corresponds to one View; identical State yields identical View.

Action

When State changes, the View updates. Users interact with the View, not the State, so View changes are always driven by State. An Action is the View’s notification that State should change. It is an object with a mandatory type property and optional additional data.

Action Creator

Each distinct Action can be generated by an Action Creator function, simplifying the creation of Action objects.

For example, addTodo is an Action Creator.

store.dispatch()

store.dispatch()

is the only way the View can send an Action to the store.

The dispatched Action is processed by reducers to produce a new State.

Reducer

After receiving an Action, the store must compute a new State. This computation is performed by a Reducer, a pure function that takes the current State and the Action as arguments and returns a new State.

combineReducers(reducers)

The combineReducers helper merges multiple reducer functions (provided as an object) into a single root reducer, which can then be passed to createStore. Each child reducer manages its slice of the State (e.g., todos and counter).

applyMiddleware(...middlewares)

applyMiddleware

takes an array of middleware functions and returns a function that enhances createStore. Each middleware receives { getState, dispatch } and returns a function that receives next, ultimately forming a chain where the last middleware receives the real store’s dispatch method.

<Provider store> and connect(...)

The <Provider store> component makes the Redux store available to all nested components that use connect(). Typically, the root component is wrapped with <Provider> to enable connect() throughout the component tree.

connect

links React components to the Redux store, allowing them to receive state and dispatch actions as props.