React ADVANCED

React Design Patterns

Advanced React patterns for state management, concurrent rendering, React 19 Actions, and Server Components

10 min read

reactpatternsreact-19concurrentserver-componentsactionsstate-managementreduceroptimistic-ui

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State Management Patterns

Patterns for managing complex state with reducers, context, and custom hooks

useReducer Pattern

Manage complex state transitions with a reducer function and dispatched actions

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💡 useReducer centralizes state logic — pure functions are easy to test in isolation

⚡ Action types should describe WHAT happened (user_added) not HOW to update (setUser)

📌 Pass an init function as the third arg for lazy initialization of expensive state

🟢 Use useReducer when state has 3+ sub-values or complex transitions — useState otherwise

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Reducer + Context Pattern

Combine useReducer with Context to share complex state across the component tree (Redux-lite)

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💡 Split state and dispatch into TWO contexts so dispatchers do not re-render on state changes

⚡ Wrap useContext in custom hooks (useTasks, useTasksDispatch) for ergonomics and type safety

📌 This is the standard "Redux without Redux" pattern — perfect for app-wide state without libraries

🟢 dispatch is stable across renders, so components that only dispatch never re-render unnecessarily

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Custom Hooks Composition

Build complex behavior by composing smaller, focused custom hooks

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💡 Custom hooks compose freely — useDebouncedSearch is just useDebounce + useFetch

⚡ Each hook should do ONE thing well — composition handles the complex cases

📌 Return objects when destructuring is more readable; arrays for tuple-like APIs

🟢 Always use the cancelled flag pattern in async effects to avoid memory leaks

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Concurrent Rendering

Use React concurrent features to keep the UI responsive during expensive updates

useTransition

Mark state updates as non-urgent transitions to keep the UI responsive

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💡 useTransition tells React "this update is not urgent — keep the UI responsive"

⚡ Use it for tab switches, search filtering, and any heavy re-render triggered by user input

📌 React 19 supports async functions inside startTransition — perfect for form submissions

🟢 isPending lets you show subtle loading hints without blocking the click feedback

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useDeferredValue

Defer rendering of expensive UI based on a value while keeping inputs responsive

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💡 useDeferredValue defers a VALUE; useTransition defers an UPDATE — pick based on what you control

⚡ Always memoize the expensive child — otherwise React still re-renders it on every keystroke

📌 Compare value !== deferredValue to detect stale state and show a visual hint

🟢 React renders twice: once with the old value, then again in the background with the new one

useDeferredValueconcurrentperformance

React 19 Actions & Forms

New form handling pattern with built-in pending state, errors, and optimistic updates

useActionState

Manage form state, errors, and pending status with a single hook

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💡 useActionState replaces the old useState dance for form loading + error handling

⚡ The action receives previousState and formData — return any state shape you need

📌 Forms work without JavaScript when paired with server actions — true progressive enhancement

🟢 Use defaultValue (not value) so the form is uncontrolled and works with form data

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useOptimistic

Show instant UI feedback while async operations are still in flight

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💡 useOptimistic shows instant feedback then reverts automatically if the action fails

⚡ Must be called inside startTransition or a form action — React enforces this

📌 Add a pending flag in the optimistic state to visually distinguish unsaved items

🟢 No manual rollback needed — React reconciles when the real state updates

useOptimisticoptimistic-uireact-19

useFormStatus & form Actions

Read pending state from a parent form without prop drilling

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💡 useFormStatus reads parent form state — perfect for SubmitButton without prop drilling

⚡ Form actions auto-reset the form after success and provide automatic pending state

📌 useFormStatus only works in CHILD components — wrap your button in its own component

🟢 Combine with useActionState for full form state management without useState

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Server Components

Render components on the server, fetch data directly, and mix with client components

Server Components Basics

Async components that run on the server with direct data access

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💡 Server Components are async, run only on the server, and never ship JS to the browser

⚡ Pass Server Components as children to Client Components — best of both worlds

📌 Props from Server → Client must be serializable: no functions, classes, or Dates

🟢 Default to Server Components and opt into Client Components only when you need interactivity

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Server Actions ('use server')

Call server functions directly from client components and forms

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💡 Server actions look like regular function calls but execute on the server with direct DB access

⚡ Use revalidatePath/revalidateTag to refresh the cached UI after a mutation

📌 Server actions in form action props give progressive enhancement — works without JavaScript

🟢 Always validate inputs in server actions — they are public endpoints accessible to anyone

server-actionsuse-servermutations

Component API Patterns

Patterns for designing flexible and reusable component APIs

Polymorphic Components (as prop)

One component that can render as different elements based on an "as" prop

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💡 The "as" prop pattern keeps semantics flexible while sharing styling and behavior

⚡ Default the "as" prop with a destructure default (as: Component = "div")

📌 Type-safe polymorphism in TypeScript needs ElementType + ComponentPropsWithoutRef

🟢 Used by every major React UI library — Radix, Chakra, Mantine, shadcn/ui

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Controlled vs Uncontrolled

Two ways to manage component state — let parent control, or manage internally

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💡 Controlled = parent owns state; Uncontrolled = DOM/component owns state

⚡ Building a component to support both is a common library pattern (Radix, MUI)

📌 React warns if you switch between controlled/uncontrolled — pick one and stick with it

🟢 react-hook-form leverages uncontrolled inputs for fewer re-renders on large forms

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Provider Pattern with Custom Hooks

Wrap context with a Provider component and a custom hook for safe consumption

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💡 The Provider + custom hook combo is the standard way to expose Context safely

⚡ Throwing in the custom hook gives clear errors when the Provider is missing

📌 Encapsulating state inside the Provider lets you refactor to Zustand/Jotai later without breaking consumers

🟢 Split state and dispatch into separate contexts to prevent unnecessary re-renders

providercontextcustom-hooks

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