In React, using TypeScript, how do I pass a ref to a custom component using RefForwardingComponent and forwardRef?

Question

I'm trying to pass a ref to a custom component (so that I can set focus to the component).

But I keep getting this error

const RefComp: React.RefForwardingComponent<HTMLInputElement, Props>
Type '{ value: string; onChange: Dispatch<SetStateAction<string>>; ref: MutableRefObject<HTMLInputElement | undefined>; }'
is not assignable to type 'IntrinsicAttributes & Props & { children?: ReactNode; }'.
  Property 'ref' does not exist on type 'IntrinsicAttributes & Props & { children?: ReactNode; }'.ts(2322)

This is my code

import * as React from 'react';
import {useRef, useState, RefForwardingComponent, forwardRef} from 'react';

interface Props {
    value: string;
    onChange(event: string): void;
}

const RefComp: RefForwardingComponent<HTMLInputElement, Props> = forwardRef<
    HTMLInputElement,
    Props
>(({value, onChange}, ref) => (
    <input
        value={value}
        onChange={event => onChange(event.target.value)}
        ref={ref}
    />
));

export default function App() {
    const [val, setVal] = useState('');
    const inputRef = useRef<HTMLInputElement>();

    return (
        <div className="App">
            <RefComp value={val} onChange={setVal} ref={inputRef} />
            <p>{val}</p>
        </div>
    );
}

Here's a codesandbox https://codesandbox.io/s/crimson-cdn-klfp5

The code seems to work fine, if I ignore the error. So not sure why I'm getting it...

Can anyone please explain why I get the error, and how I fix it? :)

EDIT:

As mentioned in the comments you can work around this by adding ref to your props.

import * as React from 'react';
import {
    useRef,
    useState,
    RefForwardingComponent,
    forwardRef,
    MutableRefObject,
} from 'react';

interface Props {
    value: string;
    onChange(event: string): void;
    ref?: MutableRefObject<HTMLInputElement | null>;
}

const RefComp: RefForwardingComponent<HTMLInputElement, Props> = forwardRef<
    HTMLInputElement,
    Props
>(({value, onChange}, ref) => (
    <input
        value={value}
        onChange={event => onChange(event.target.value)}
        ref={ref}
    />
));

export default function App() {
    const [val, setVal] = useState('');
    const inputRef = useRef<HTMLInputElement>(null);

    return (
        <div className="App">
            <RefComp value={val} onChange={setVal} ref={inputRef} />
            <p>{val}</p>
        </div>
    );
}

But this feels wrong. Now we're saying we have ref both as parts of the props, and as a second callback argument to the function passed to forwardRef

My issue with this would probably be clearer if I wrote it like this

const RefComp: RefForwardingComponent<HTMLInputElement, Props> = forwardRef<
    HTMLInputElement,
    Props
>((props: Props, ref) => (
    <input
        value={props.value}
        onChange={event => props.onChange(event.target.value)}
        ref={ref /* here, props.ref is also available, but wouldn't work */ }
    />
));

EDIT 2:

Here's a related question

Typescript RefForwardingComponent not working

EDIT 3:

I found the relevant source code. https://github.com/DefinitelyTyped/DefinitelyTyped/blob/33f6179e0f25b0ca798ad89a667c0a27ea0c98dd/types/react/index.d.ts#L702

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

So the forwardRef function returns a component of type ForwardRefExoticComponent<PropsWithoutRef<P> & RefAttributes<T>>. This is a component that takes props of type PropsWithoutRef<P> intersected with RefAttributes<T>. Both types are also defined in the same file.

From what I understand the first one basically just excludes ref from P (which is Props in my original example). The second one is defined as

interface RefAttributes<T> extends Attributes {
    ref?: Ref<T>;
}

Given this information I really don't understand why I have to add ref to my own Props. It really looks as if forwardRef should do it for me - even going as far as actually removing ref from my own Props...

Can someone please explain what's going on here?

Answer 1

The problem was a bad type definition for RefComp. Removing that (letting TypeScript infer the type instead) and the code works just fine.

import * as React from 'react';
import {useRef, useState, forwardRef} from 'react';

interface Props {
    value: string;
    onChange(event: string): void;
}

const RefComp = forwardRef<HTMLInputElement, Props>(
    ({value, onChange}, ref) => (
        <input
            value={value}
            onChange={event => onChange(event.target.value)}
            ref={ref}
        />
    ),
);

export default function App() {
    const [val, setVal] = useState('');
    const inputRef = useRef<HTMLInputElement>(null);

    React.useEffect(() => {
        if (inputRef.current) {
            inputRef.current.focus();
        }
    }, []);

    return (
        <div className="App">
            <RefComp value={val} onChange={setVal} ref={inputRef} />
            <p>{val}</p>
        </div>
    );
}

https://codesandbox.io/s/quizzical-liskov-bsruh