JSX.Element vs ReactElement vs ReactNode
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These three types usually confuse novice React developers. It seems like they are the same thing, just named differently.
But it's not quite right.
JSX.Element
vs ReactElement
Both types are the result of React.createElement()
/jsx()
function call.
They are both objects with:
- props
- a couple of other "hidden" properties, like ref, $$typeof, etc
ReactElement
ReactElement
type is the most basic of all. It's even defined in React source code using flow!
// ./packages/shared/ReactElementType.js
export type ReactElement = {|
$$typeof: any,
type: any,
key: any,
ref: any,
props: any,
// ReactFiber
_owner: any,
// __DEV__
_store: {validated: boolean, ...},
_self: React$Element<any>,
_shadowChildren: any,
_source: Source,
|};
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This type is also defined in DefinitelyTyped package.
interface ReactElement<P = any, T extends string | JSXElementConstructor<any> = string | JSXElementConstructor<any>> {
type: T;
props: P;
key: Key | null;
}
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JSX.Element
It's more generic type. The key difference is that props
and type
are typed as any
in JSX.Element
.
declare global {
namespace JSX {
interface Element extends React.ReactElement<any, any> { }
// ...
}
}
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This gives flexibility in how different libraries implement JSX.
For example, Preact has its own implementation with different API.
ReactNode
ReactNode
type is a different thing. It's not a return value of React.createElement()
/jsx()
function call.
const Component = () => {
// Here it's ReactElement
return <div>Hello world!</div>
}
// Here it's ReactNode
const Example = Component();
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React node itself is a representation of the virtual DOM. So ReactNode
is the set of all possible return values of a component.
type ReactChild = ReactElement | ReactText;
type ReactFragment = {} | Iterable<ReactNode>;
interface ReactPortal extends ReactElement {
key: Key | null;
children: ReactNode;
}
type ReactNode =
| ReactChild
| ReactFragment
| ReactPortal
| boolean
| null
| undefined;
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What to use for children
?
Generally speaking, ReactNode
is the correct way to type the children
prop. It gives the most flexibility while maintaining the proper type checking.
But it has a caveat, because ReactFragment
allows a {}
type.
const Item = ({ children }: { children: ReactNode }) => {
return <li>{children}</li>;
}
const App = () => {
return (
<ul>
// Run-time error here, objects are not valid children!
<Item>{{}}</Item>
</ul>
);
}
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Learn from the best!
Where factory pattern is used in JavaScript?
JS is a multi-paradigm programming language, so it provides a lot of different ways to deal with the same problem.
👇
#javascript #FrontEnd #programming18:09 PM - 07 Feb 2022
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