React with Typescript -- Generics while using React.forwardRef
Solution 1:
Creating a generic component as output of React.forwardRef
is not directly possible 1 (see bottom). 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 }
]
Choose variants (1) or (2) for simplicity. (3) will replace forwardRef
by usual props. With (4) you globally chance forwardRef
type definitions once in the app.
1. Use type assertion ("cast")
// Given render function (input) for React.forwardRef
const FRefInputComp = <T extends Option>(p: Props<T>, ref: Ref<HTMLDivElement>) =>
<div ref={ref}> {p.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 might add an extra type to make the assertion simpler:
type ForwardRefFn<R> = <P={}>(p: P & React.RefAttributes<R>) => ReactElement |null
// `RefAttributes` is built-in type with ref and key props defined
const Comp12 = React.forwardRef(FRefInputComp) as ForwardRefFn<HTMLDivElement>
const Usage12 = () => <Comp12 options={options} ref={myRef} />
2. Wrap forwarded component
const FRefOutputComp2 = React.forwardRef(FRefInputComp)
// ↳ T is instantiated with base constraint `Option<unknown>` from FRefInputComp
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 forwardRef
alltogether
Use a custom ref prop instead. This one is my favorite - simplest alternative, a legitimate way in React and doesn't need 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} />
4. Use global type augmentation
Add following code once in your app, perferrably in a separate module react-augment.d.ts
:
import React from "react"
declare module "react" {
function forwardRef<T, P = {}>(
render: (props: P, ref: ForwardedRef<T>) => ReactElement | null
): (props: P & RefAttributes<T>) => ReactElement | null
}
This will augment React module type declarations, overriding forwardRef
with a new function overload type signature. Tradeoff: component properties like displayName
now need a type assertion.
1 Why does the original case not work?
React.forwardRef
has following type:
function forwardRef<T, P = {}>(render: ForwardRefRenderFunction<T, P>):
ForwardRefExoticComponent<PropsWithoutRef<P> & RefAttributes<T>>;
So this function takes a generic component-like render function ForwardRefRenderFunction
, and returns the final component with type ForwardRefExoticComponent
. These two are just function type declarations with additional properties displayName
, defaultProps
etc.
Now, there is a TypeScript 3.4 feature called higher order function type inference akin to Higher-Rank Types. It basically allows you to propagate free type parameters (generics from the input function) on to the outer, calling function - React.forwardRef
here -, so the resulting function component is still generic.
But this feature can only work with plain function types, as Anders Hejlsberg explains in [1], [2]:
We only make higher order function type inferences when the source and target types are both pure function types, i.e. types with a single call signature and no other members.
Above solutions will make React.forwardRef
work with generics again.
Playground variants 1, 2, 3
Playground variant 4