Understanding State Types in Scalable React Apps

As React applications scale, the complexity of state management often increases faster than the component structure. A small set of local state variables can quickly become a complex mix of interdependent client state, server responses, derived values, and shared data used throughout the application. Without a clear way to categorize state, developers tend to overuse global stores, duplicate data in multiple places, or elevate state to the wrong level in the component hierarchy. Over time, these issues reduce code clarity, introduce unnecessary re-renders, and make state behavior harder to reason about.

To avoid this, a scalable React architecture starts by identifying the type of state before deciding where it should live. Not all state serves the same purpose, have the same performance cost, or belong at the same level of the component tree.

Four fundamental state types in React

To scale a React application effectively, it’s crucial to understand that there isn’t just one “type” of state. Categorizing states helps you choose the right tool for the right job, which is crucial for building a scalable and maintainable application. The four core state types described below form the foundation upon which every advanced React pattern is built. Each type has distinct characteristics, responsibilities, and architectural implications.

Local (or UI) state

This is a state that “belongs” to a single component or a small group of related components.

• What it is: Data that controls a component’s internal behavior. Think of a form input’s current value, whether a modal is open or closed, or which tab is currently active.

• How to manage it: Typically, it’s managed with the useState or useReducer Hooks.

• Scalability impact: This is the simplest and most performant state. As applications scale, a good default is to keep state local for as long as it remains practical. Only promote the state to a global store when it needs to be shared across unrelated parts of the app.

Global (or app) state

This is a state that needs to be accessed and updated by many different components, often in different parts of your application tree.

• What it is: Data that your whole app cares about. Common examples include the logged-in user’s information, the app’s theme (dark/light mode), or the contents of a shopping cart.

• How to manage it:

  • Simple: React’s built-in Context API (good for low-frequency updates, like theme).

  • Complex: Dedicated state management libraries like Redux, Zustand, or Jotai.

• Scalability impact: This is where many scaling problems live. Using useState at the top level and passing props down (known as prop drilling) becomes difficult to maintain. Using Context API for everything can cause performance issues, as all-consuming components re-render on any state change.

  • To scale, you must choose a global state tool that fits your needs. Libraries like Zustand are popular because they are simple and prevent unnecessary re-renders, making them highly scalable.

Server (or asynchronous) state

This distinction becomes important as applications scale. The application does not own this state and represents a local copy of data stored on a server or in a database.

• What it is: This is any data you fetch from an API. This state also includes its metadata, such as isLoading, isError, isSuccess, and isFetching.

• How to manage it: You should avoid managing this in a global state (like Redux) if possible. This is a common mistake that leads to complex, manual logic for caching, re-fetching, and synchronizing.

• Scalability impact: This is arguably the most important category for performance and user experience. Using a dedicated library is a non-negotiable for a scalable app.

  • To scale, use a tool like React Query or SWR. These libraries handle caching, background refetching, and stale-data management for you, dramatically simplifying your code and making your app feel much faster.

Derived state

This is not a state storage location. It is a pattern for deriving values from the existing state.

• What it is: Data that is calculated or computed from another piece of state. Examples include: a “full name” derived from “firstName” and “lastName,” or a “total price” calculated from the items in a shopping cart.

• How to manage it: You don’t store it in useState. Instead, you calculate it directly during render. If the calculation is very expensive, you memoize it using the useMemo hook.

• Scalability impact: This is a critical pattern for scaling. Storing derived data in its own state variable (e.g., useState) creates synchronization bugs, where your “total price” might be out of sync with the “cart items.” By deriving it, you ensure you always have a single source of truth, and your UI is always consistent, which is essential for maintainable code.