React with Typescript — Generics while using React.forwardRef

问题

I am trying to create a generic component where a user can pass the a custom OptionType to the component to get type checking all the way through. This component also required a React.forwardRef.

I can get it to work without a forwardRef. Any ideas? Code below:

WithoutForwardRef.tsx

export interface Option<OptionValueType = unknown> {
  value: OptionValueType;
  label: string;
}

interface WithoutForwardRefProps<OptionType> {
  onChange: (option: OptionType) => void;
  options: OptionType[];
}

export const WithoutForwardRef = <OptionType extends Option>(
  props: WithoutForwardRefProps<OptionType>,
) => {
  const { options, onChange } = props;
  return (
    <div>
      {options.map((opt) => {
        return (
          <div
            onClick={() => {
              onChange(opt);
            }}
          >
            {opt.label}
          </div>
        );
      })}
    </div>
  );
};

WithForwardRef.tsx

import { Option } from './WithoutForwardRef';

interface WithForwardRefProps<OptionType> {
  onChange: (option: OptionType) => void;
  options: OptionType[];
}

export const WithForwardRef = React.forwardRef(
  <OptionType extends Option>(
    props: WithForwardRefProps<OptionType>,
    ref?: React.Ref<HTMLDivElement>,
  ) => {
    const { options, onChange } = props;
    return (
      <div>
        {options.map((opt) => {
          return (
            <div
              onClick={() => {
                onChange(opt);
              }}
            >
              {opt.label}
            </div>
          );
        })}
      </div>
    );
  },
);

App.tsx

import { WithoutForwardRef, Option } from './WithoutForwardRef';
import { WithForwardRef } from './WithForwardRef';

interface CustomOption extends Option<number> {
  action: (value: number) => void;
}

const App: React.FC = () => {
  return (
    <div>
      <h3>Without Forward Ref</h3>
      <h4>Basic</h4>
      <WithoutForwardRef
        options={[{ value: 'test', label: 'Test' }, { value: 1, label: 'Test Two' }]}
        onChange={(option) => {
          // Does type inference on the type of value in the options
          console.log('BASIC', option);
        }}
      />
      <h4>Custom</h4>
      <WithoutForwardRef<CustomOption>
        options={[
          {
            value: 1,
            label: 'Test',
            action: (value) => {
              console.log('ACTION', value);
            },
          },
        ]}
        onChange={(option) => {
          // Intellisense works here
          option.action(option.value);
        }}
      />
      <h3>With Forward Ref</h3>
      <h4>Basic</h4>
      <WithForwardRef
        options={[{ value: 'test', label: 'Test' }, { value: 1, label: 'Test Two' }]}
        onChange={(option) => {
          // Does type inference on the type of value in the options
          console.log('BASIC', option);
        }}
      />
      <h4>Custom (WitForwardRef is not generic here)</h4>
      <WithForwardRef<CustomOption>
        options={[
          {
            value: 1,
            label: 'Test',
            action: (value) => {
              console.log('ACTION', value);
            },
          },
        ]}
        onChange={(option) => {
          // Intellisense SHOULD works here
          option.action(option.value);
        }}
      />
    </div>
  );
};

In the App.tsx, it says the WithForwardRef component is not generic. Is there a way to achieve this?

Example repo: https://github.com/jgodi/generics-with-forward-ref

Thanks!

回答1:

Creating a generic component as output of React.forwardRef is not directly possible¹ (see bottom for further info). There are some alternatives though - let's simplify your example a bit for illustration:

type Option<O = unknown> = {
    value: O;
    label: string;
}
type Props<T extends Option<unknown>> = { options: T[] }

const options = [
  { value: 1, label: "la1", flag: true }, 
  { value: 2, label: "la2", flag: false }
] // just some options data

1. Cast it

// Given input comp for React.forwardRef
const FRefInputComp = <T extends Option>(props: Props<T>, ref: Ref<HTMLDivElement>) =>
    <div ref={ref}> {props.options.map(o => <p>{o.label}</p>)} </div>

// Cast the output
const FRefOutputComp1 = React.forwardRef(FRefInputComp) as
    <T extends Option>(p: Props<T> & { ref?: Ref<HTMLDivElement> }) => ReactElement

const Usage11 = () => <FRefOutputComp1 options={options} ref={myRef} />
// options has type { value: number; label: string; flag: boolean; }[] 
// , so we have made FRefOutputComp generic!

This works, as the return type of forwardRef in principle is a plain function. We just need a generic function type shape. You could an extra type to make the assertion simpler:

type ForwardRefFn<R> = <P = {}>(p: P & React.RefAttributes<R>) => ReactElement | null
// RefAttributes is built-in with ref and key props defined
const Comp12 = React.forwardRef(FRefInputComp) as ForwardRefFn<HTMLDivElement>
const Usage12 = () => <Comp12 options={options} ref={myRef} />

2. Wrap it

const FRefOutputComp2 = React.forwardRef(FRefInputComp)
// T is replaced by its constraint Option<unknown> in FRefOutputComp2

export const Wrapper = <T extends Option>({myRef, ...rest}:
    Props<T> & {myRef: React.Ref<HTMLDivElement>}) => <FRefOutputComp2 {...rest} ref={myRef} />

const Usage2 = () => <Wrapper options={options} myRef={myRef} />

3. Omit it (use custom ref prop)

This one is my favorite - simplest alternative, a legitimate way in React and doesn't use forwardRef.

const Comp3 = <T extends Option>(props: Props<T> & { myRef: Ref<HTMLDivElement> }) =>
    <div ref={myRef}> {props.options.map(o => <p>{o.label}</p>)} </div>
const Usage3 = () => <Comp3 options={options} myRef={myRef} />

---

¹ The type declaration of React.forwardRef is:

function forwardRef<T, P = {}>(Component: RefForwardingComponent<T, P>): ...

So it takes a generic component interface, whose type parameters T, P must be concrete. In other words: RefForwardingComponent is not a generic function declaration, so higher order function type inference cannot propagate free type parameters on to the calling function React.forwardRef.

---

Playground

来源：https://stackoverflow.com/questions/58469229/react-with-typescript-generics-while-using-react-forwardref