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Define a React function component by giving its props an object type, then accept that type as the function’s parameter. TypeScript infers many values from context and initial values, so add annotations where they clarify the component’s intended API or inference is insufficient. This guide covers the setup, prop and child types, event handlers, Hooks, and safe state updates.
Set up TypeScript for React JSX
Use the .tsx extension for each TypeScript file that contains JSX. For React web type definitions, install @types/react and @types/react-dom. The TypeScript configuration also needs DOM library types; dom is included by default if lib is omitted. Set jsx to a valid compiler option; preserve is sufficient for many applications. See the React TypeScript guide and, for published libraries, the TypeScript JSX configuration documentation.
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There is no single setup command that fits every React framework. Follow the current installation guide for the framework you use, then check that its TypeScript configuration covers the JSX and DOM requirements.
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A component’s props are an object-shaped input contract. Define that shape with either a type alias or an interface, and use it as the function parameter type:
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interface GreetingProps {
name: string;
excited?: boolean;
}
function Greeting({ name, excited = false }: GreetingProps) {
return <h1>{excited ? `Hello, ${name}!` : `Hello, ${name}`}</h1>;
}Here, name is required and excited is optional. The default value in the parameter list is ordinary JavaScript destructuring; it does not replace the props type. A type alias describes this same object shape equally well. Choose the form that fits your team’s conventions and how you need to compose or extend the type.
Inline or named props?
An inline object annotation can be concise when a component has only a tiny, one-off prop shape. A named type or interface is easier to scan when props include several fields, need reuse, or benefit from a descriptive name. This is an API clarity choice, not a performance optimization.
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Represent limited alternatives with unions
When a prop may take only specific values, a union makes those alternatives explicit—for example, type Status = "loading" | "success" | "error". Consumers then get type checking against the declared options rather than an unrestricted string.
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Pick the children type based on what the component is designed to accept. React.ReactNode is broad: it covers the range of values React accepts as JSX children, including text and numbers. React.ReactElement is narrower and represents a JSX element, not primitive text or numeric children.
interface PanelProps {
children: React.ReactNode;
}
function Panel({ children }: PanelProps) {
return <section>{children}</section>;
}TypeScript cannot use these types to require that children be a particular JSX tag, such as requiring only <li> children. The type describes the value category, not a specific tag name.
Type event handlers and style props
When a handler is written inline in JSX, TypeScript can often infer its event type from the element and callback position. If you extract the handler into a separate function, annotate its parameter when inference does not provide the type you need. For an input change event, React’s guide uses React.ChangeEvent<HTMLInputElement>:
function handleChange(event: React.ChangeEvent<HTMLInputElement>) {
console.log(event.currentTarget.value);
}React also provides event-handler aliases, such as React.ChangeEventHandler<HTMLInputElement>. For less common event types, React.SyntheticEvent is the base event type. For a prop that accepts an inline style object, use React.CSSProperties.
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Let TypeScript infer Hook types where it can
React’s Hook type definitions work with TypeScript inference. For example, useState(false) infers a boolean state value and a setter that accepts booleans. Context takes its value type from the value passed to createContext or from an explicit generic. A memoized value is inferred from the return value of its callback.
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Add an explicit type argument or annotation when the initial value does not express the full state domain or inference misses your intent. For example, a state initialized to null may later hold an object, so declare that wider domain rather than letting the initializer define the whole type:
const [user, setUser] = useState<User | null>(null);In strict TypeScript, a callback parameter passed to useCallback may need an explicit type. A React handler alias can express the input event and element together:
const handleChange: React.ChangeEventHandler<HTMLInputElement> = (event) => {
setQuery(event.currentTarget.value);
};Call Hooks only at the top level
Hooks are not general-purpose functions that can be called wherever convenient. Call them only at the top level of a function component or custom Hook, before any early return. Do not call Hooks in conditions, loops, nested functions, event handlers, try/catch/finally blocks, or class components. React’s Rules of Hooks explain the restrictions; the eslint-plugin-react-hooks plugin can help catch violations.
Keep rendering pure and update state through its setter
A component should render from its inputs without changing the outside world: the same props and state should produce the same output, while side effects belong outside render. Treat props and state as immutable snapshots. Do not change an object received through props or directly assign to a state variable. Instead, derive a copy when needed and use the setter returned by useState to request an update. Directly changing a local state variable does not notify React to render again. See React’s purity rules.
Function components and class components
React’s documentation says, “We recommend defining components as functions instead of classes.” Class components remain documented and supported, but they receive props through this.props; function components receive props as parameters. Hooks cannot be used inside class components. See the official Component reference.
Quick Recap
Common typing choices at a glance
| Decision | Use this when | What it communicates |
|---|---|---|
| Inline props object | The prop shape is small and used once | A concise input contract |
Named type or interface |
The component has several props, the shape is reused, or it needs a clear name | A reusable, documented input contract |
React.ReactNode |
The component accepts broad JSX child values, including text or numbers | A broad children API |
React.ReactElement |
The component requires a JSX element rather than primitive children | A narrower children API |
| Inferred Hook type | The initializer or callback return already expresses the intended type | The type follows from the value |
| Explicit Hook type or annotation | The intended domain is broader than the initializer or callback inference is insufficient | An explicit state or callback contract |
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