React v19 operator

Look up React commands, project structure, rendering patterns, and focused operations across components and composition, state and context, effects and refs, forms and actions, performance and testing. Use when the user wants a concise reference instead of a guided workflow.

Create and refactor React function components, JSX, props, children, composition, context boundaries, and reusable component APIs. Use when building components, splitting or combining UI, repairing prop contracts, or reviewing composition.

Design and repair React effects, effect dependencies, cleanup, refs, imperative handles, subscriptions, timers, and external-system synchronization. Use when effects loop, run twice, leak, use stale values, or a component must coordinate with a non-React system.

Inspect the installed React versions, package manager, renderer or router mode, source tree, build configuration, scripts, and target environments without changing anything. Use before React work, when conventions are unknown, or when the user asks what is configured.

Build React forms and actions with native semantics, controlled or uncontrolled inputs, validation, async submission, pending state, optimistic updates, and server error recovery. Use when creating a form, fixing field state, adding async actions, or handling validation and optimistic updates.

Connect React to styling, data sources, tests, browser and server runtimes, build tools, CI, observability, and deployment while preserving component and execution boundaries. Use when React crosses another subsystem or must behave consistently through production.

Measure and improve React rendering performance and test component behavior using Profiler evidence, memoization, Suspense boundaries, interaction tests, and bundle inspection. Use when renders are slow, memoization is proposed, Suspense behavior is wrong, or component tests need reliable coverage.

Install and configure React from zero with project-local dependencies, explicit rendering and runtime boundaries, source structure, baseline checks, and one verified feature. Use when a project has no React setup or the user explicitly asks to initialize it.

Operate React state ownership, derived state, reducers, controlled and uncontrolled components, context, keys, and preservation or reset behavior. Use when state is duplicated, stale, unexpectedly reset, shared across components, or difficult to update.

Diagnose React failures involving versions, rendering, state, hydration, routing, caching, async behavior, build output, tests, integrations, and performance without masking the original error. Use when React fails a check, behaves differently across environments, or renders unexpected output.