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Pass a value to a React component by adding it as an attribute in JSX; the receiving component reads it from its props object or destructures it in its parameter.
Pass a value as a prop
In React, a parent component supplies data to a child through props. Put the value on the child’s JSX tag. Use braces when the value is a JavaScript expression rather than a plain string.
function Profile() {
const person = { name: 'Lin Lanying', imageId: '1bX5QH6' };
return <Avatar person={person} size={100} />;
}
function Avatar({ person, size }) {
return <img alt={person.name} width={size} height={size} />;
}Here, Profile passes an object as person and a number as size. In JSX, the braces around person tell React to evaluate the JavaScript variable. To pass an object literal directly, use two pairs of braces: <Avatar person={{ name: 'Lin' }} />. The outer pair enters JavaScript expression syntax; the inner pair creates the object.
A function component receives a single props object. Destructuring in the parameter is shorthand for reading its properties:
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function Avatar(props) {
const person = props.person;
return <img alt={person.name} />;
}Both forms read the same prop. Props can hold strings, numbers, objects, arrays, and functions. For the official walkthrough, see React’s Passing Props to a Component.
Set a default for an optional prop
Destructure a prop with a default value when the caller may omit it:
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function Avatar({ size = 100 }) {
return <img width={size} height={size} />;
}This default is used when size is missing or undefined. It does not replace null or 0; those values are passed through as supplied.
Pass nested JSX as children
When a component wraps content chosen by its caller, nest that content between its opening and closing tags:
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function Card({ children }) {
return <section className="card">{children}</section>;
}
function Profile() {
return (
<Card>
<Avatar size={100} />
</Card>
);
}The nested JSX is received by Card as its children prop. This pattern lets a wrapper control layout while the caller chooses what appears inside it. React’s props guide covers children alongside other prop patterns.
Forward props when appropriate
You can spread an existing props object onto another component:
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function Profile({ avatarProps }) {
return <Avatar {...avatarProps} />;
}This forwards the properties in avatarProps to Avatar. Spreading can reduce repetitive forwarding, but it also makes the receiving component’s inputs less obvious at the call site. Prefer explicit attributes when they make the interface easier to understand, such as <Avatar size={100} person={person} />.
Use a callback prop for child-to-parent interactions
Props flow from parent to child, but a child can notify its parent by calling a function the parent passes in. The parent owns the state and supplies updated values when it renders again:
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function Counter() {
const [count, setCount] = useState(0);
return <CounterButton count={count} onIncrement={() => setCount(count + 1)} />;
}
function CounterButton({ count, onIncrement }) {
return <button onClick={onIncrement}>Count: {count}</button>;
}The callback gives the child a way to request an update; the child should not change a received prop directly. React describes props as “read-only snapshots in time: every render receives a new version of props” in its props documentation.
Choose props, spread, or Context
| Approach | Best fit | Trade-off |
|---|---|---|
| Explicit props | A small, local parent-to-child interface | Inputs are visible on the JSX tag. |
| Spread forwarding | Passing an existing group of props through to another component | It can hide which values the receiving component gets. |
| Context | A value needed by many descendants, especially when passing it through intermediate components is inconvenient | It avoids threading that value through each intermediate component; use it when ordinary props become cumbersome. |
Start with explicit props for data needed by a nearby child. If many descendants need the same value, or intermediate components only pass it along, consider React Context. The React guide to passing data deeply with Context explains that option.
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