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I'm writing a React component which can forward ref to its chilren

I found out that for the return type of the function components, I can use ForwardRefExoticComponent and ForwardRefRenderFunction. But I'm not sure whats the difference between them.

So far, When using ForwardRefExoticComponent, I can extend it while the ForwardRefRenderFunction cannot? I posted a question related to my case here : How to export forwardRef with ForwardRefRenderFunction

If anyone know whats the difference between them and what they do please help me. Because it seems that React team has no document about them (but they are inside react package)

Answers

ForwardRefExoticComponent

The definition taken from here is

interface ExoticComponent<P = {}> {
    /**
     * **NOTE**: Exotic components are not callable.
     */
    (props: P): (ReactElement|null);
    readonly $$typeof: symbol;
}

interface NamedExoticComponent<P = {}> extends ExoticComponent<P> {
    displayName?: string;
}

interface ForwardRefExoticComponent<P> extends NamedExoticComponent<P> {
    defaultProps?: Partial<P>;
    propTypes?: WeakValidationMap<P>;
}

If you write it out you get

interface ForwardRefExoticComponent<P> {
    /**
     * **NOTE**: Exotic components are not callable.
     */
    (props: P): (ReactElement|null);
    readonly $$typeof: symbol;
    displayName?: string;
    defaultProps?: Partial<P>;
    propTypes?: WeakValidationMap<P>;
}

ForwardRefRenderFunction

The definition taken from here is

interface ForwardRefRenderFunction<T, P = {}> {
    (props: PropsWithChildren<P>, ref: ((instance: T | null) => void) | MutableRefObject<T | null> | null): ReactElement | null;
    displayName?: string;
    // explicit rejected with `never` required due to
    // https://github.com/microsoft/TypeScript/issues/36826
    /**
     * defaultProps are not supported on render functions
     */
    defaultProps?: never;
    /**
     * propTypes are not supported on render functions
     */
    propTypes?: never;
}

Differences

• ForwardRefRenderFunction does not support propTypes and defaultProps, whereas ForwardRefExoticComponent does.
• ForwardRefExoticComponent has an additional member $$typeof of type symbol
• The call signature of ForwardRefRenderFunction takes a props object, which must include a member children and a ref object as parameters, whereas the call signature of ForwardRefExoticComponent only takes a props object of arbitrary shape as parameter.

Some more thoughts

The interplay of those two definitions is best seen in the definition of the forwardRef function:

function forwardRef<T, P = {}>(render: ForwardRefRenderFunction<T, P>): ForwardRefExoticComponent<PropsWithoutRef<P> & RefAttributes<T>>;

Also, a big difference between the two definitions seems to be, that ForwardRefExoticComponent (like all exotic components) are no function components, but actually just objects, which are treated specially when rendering them. Therefore the comment

NOTE: Exotic components are not callable.

And for some reason, those exotic components are necessary in some places.