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To write a React function component in TypeScript, put JSX in a .tsx file and describe its inputs with a props object type. TypeScript can infer many Hook types and JSX event types; add annotations where inference does not capture the component’s intended API. This guide covers setup, props, children, events, styles, Hooks, and safe state updates.
Set up a TypeScript file for React
Use the .tsx extension for every TypeScript file that contains JSX. React’s TypeScript guide identifies @types/react and @types/react-dom as the React web type definitions. Your TypeScript configuration also needs the DOM library types and a valid jsx compiler option. If lib is omitted, the DOM library is included by default; jsx: "preserve" is sufficient in many app setups. See the React TypeScript guide and check your framework’s current installation guide for framework-specific setup. Library authors should use the TypeScript JSX configuration guidance for their publishing setup.
Define props and write a function component
A component’s props form an object input contract. Describe that object with either a type alias or an interface, then use it to annotate the function parameter. Destructuring the fields in the parameter is ordinary JavaScript syntax.
interface GreetingProps {
name: string;
excited?: boolean;
}
function Greeting({ name, excited = false }: GreetingProps) {
return <h1>{excited ? `Hello, ${name}!` : `Hello, ${name}`}</h1>;
}Here, name is required, while excited is optional. The default value false applies when that prop is omitted; it does not change the declared prop type. React’s guide accepts either type or interface for prop objects. Choose the form that fits your team’s conventions and how you intend to compose or extend the type.
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Inline types or named prop types?
An inline object annotation can be concise for a component with a tiny, one-off API. A named type or interface is easier to scan when there are several fields, when the shape is reused, or when a name helps document the component’s contract. These are clarity and maintenance choices, not performance choices.
Type children to match the component’s API
Use React.ReactNode when the component accepts the broad range of values React renders as children, including text and numbers. Use React.ReactElement when the API should accept a JSX element rather than primitive text or numbers.
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interface PanelProps {
children: React.ReactNode;
}
function Panel({ children }: PanelProps) {
return <section>{children}</section>;
}TypeScript cannot use these types to require that a child be a particular JSX tag, such as <li>. Pick the broadness your component actually supports instead of treating a child type as a guarantee about its tag.
Type event handlers and inline styles
When a handler is written inline in JSX, TypeScript can often infer the event type from the element. For an extracted input change handler, annotate the event with React.ChangeEvent<HTMLInputElement>:
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function SearchBox() {
function handleChange(event: React.ChangeEvent<HTMLInputElement>) {
console.log(event.currentTarget.value);
}
return <input onChange={handleChange} />;
}React also provides event-handler aliases, including React.ChangeEventHandler<HTMLInputElement>, which can be useful when typing a handler variable or callback. For less common events, React.SyntheticEvent is the base event type. For a component prop that accepts an inline CSS style object, use React.CSSProperties.
interface BadgeProps {
style?: React.CSSProperties;
}Let TypeScript infer Hook types where it can
React’s Hook definitions work with TypeScript inference. For example, useState(false) infers a boolean state value and a setter for that state. Context derives its value type from the value passed to createContext or from its generic type argument, and a memoized value is inferred from the callback’s return value.
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Add an explicit type argument or annotation when the initial value or inferred return type does not express the full domain you intend. In strict TypeScript, a callback parameter may need an annotation; React’s guide demonstrates the event-handler alias React.ChangeEventHandler<HTMLInputElement> for a callback that handles an input change. Prefer inference when it accurately describes the API rather than adding annotations mechanically.
Call Hooks only at the top level
Call Hooks only at the top level of a function component or custom Hook, and do so before any early return. Do not call them inside conditions, loops, nested functions, event handlers, try/catch/finally blocks, or class components. The Rules of Hooks explain the requirement; the eslint-plugin-react-hooks plugin can help catch violations.
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Keep rendering pure and update state through its setter
React expects components and Hooks to be pure: for the same inputs, rendering should produce the same output, and side effects should happen outside render. Props and state are immutable snapshots. Do not mutate an object received through props or change a state variable directly. Create a derived copy when needed, and update state with the setter returned by useState; changing the local state variable directly does not notify React to render again. See React’s rules for components and Hooks.
Function components and class components
React recommends function components: “We recommend defining components as functions instead of classes.” Class components remain documented and supported, but their props are accessed through this.props; function components receive props as parameters. Hooks are not supported inside class components. For the class API, see the React Component reference.
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