Component Types

Component Types have syntax similar to our runtime Component Syntax to make it easy to describe the type of a component. Component Types are most useful for writing library definitions.

Specifying Props​

To declare a Component Type you can use the component keyword and list out the props your component expects.

import * as React from 'react';


type ComponentType = component(numberProp: number, optionalProp?: string);


declare const Component: ComponentType;


<Component numberProp={3} />; // OK! optionalProp is optional

Like Component Syntax, Component Types also accept a rest parameter:

import * as React from 'react';


type StarProps = {color: string, size: number};


// The ...StarProps rest parameter spreads in every prop of StarProps, so
// BlueStarType accepts specificProp plus color and size.
type BlueStarType = component(specificProp: string, ...StarProps);

Like Component Syntax, you can also declare an inline ref prop (but not in your rest parameter):

import * as React from 'react';
import {useRef} from 'react';


type ComponentWithRef = component(someProp: number, ref: React.RefSetter<number>);


declare const Component: ComponentWithRef;


component Example() {
    const ref = useRef<number | null>(null);
    return <Component someProp={42} ref={ref}/>;
}

Specifying Render Types​

You can also specify the Render Type for your component just like you can with Component Syntax

import * as React from 'react';


component Foo() { return null }
type ComponentWithRenders = component() renders Foo;


declare const Component: ComponentWithRenders;
<Component /> as renders Foo; // OK!

Polymorphic Component Types​

You can also write polymorphic Component Types, which is helpful for declaring "transparent" components:

import * as React from 'react';


declare const TransparentComponent: component<T extends React.Node>(children: T) renders T;


component Example() { return null }


const element: renders Example = (
    <TransparentComponent>
        <Example />
    </TransparentComponent>
); // OK!

Annotating Components with Component Types​

Here's how you can describe the type of a Component Syntax component using a Component Type:

import * as React from 'react';


component Foo() { return null }


component Example(someProp: number, ref: React.RefSetter<number>) renders Foo {
    return <Foo />;
}


Example as component(someProp: number, ref: React.RefSetter<number>) renders Foo; // OK!




component PolymorphicExample<T extends React.Node>(children: T) renders T {
    return children;
}


PolymorphicExample as component<T extends React.Node>(children: T) renders T; // OK!

See Also​

• Generics — generic type parameters used in component type signatures
• Library Definitions — declaring component types in library definition files