NextJS dynamic import issue

Question

I'm facing a really strange issue with dynamic import from NextJS .

I'm importing a component like so:

const Spinner = dynamic(() => import('components/ui/Spinner').then(mod => mod.Spinner))

And the Spinner.tsx is

import {useEffect, useState} from 'react'
import PulseLoader from 'react-spinners/PulseLoader'

import {FadeHOC} from '.'
import theme from 'utils/theme'


interface Props {
  inline?: boolean
}

const TIMEOUT = 1000

export const Spinner = ({inline}: Props) => {

  const [show, setShow] = useState(false)

  useEffect(() => {
    
    const timeout = setTimeout(
      () => setShow(true),
      TIMEOUT
    )
    
    return () => clearTimeout(timeout)
  }, [])

  return (
    show
      ? <FadeHOC>
          <PulseLoader size={10} margin={3} color={theme.color} css={inline ? 'margin-left: 14px;' : 'display: block; text-align: center; margin: 100px auto;'} />
        </FadeHOC>
      : null
  )
}

And on the dynamic import statement I get a TypeScript complaint:

Argument of type '() => Promise<(({ inline }: Props) => JSX.Element) | ComponentClass<never, any> | FunctionComponent<never> | { default: ComponentType<never>; }>' is not assignable to parameter of type 'DynamicOptions<{}> | Loader<{}>'.
  Type '() => Promise<(({ inline }: Props) => JSX.Element) | ComponentClass<never, any> | FunctionComponent<never> | { default: ComponentType<never>; }>' is not assignable to type '() => LoaderComponent<{}>'.
    Type 'Promise<(({ inline }: Props) => Element) | ComponentClass<never, any> | FunctionComponent<never> | { default: ComponentType<never>; }>' is not assignable to type 'LoaderComponent<{}>'.
      Type '(({ inline }: Props) => Element) | ComponentClass<never, any> | FunctionComponent<never> | { default: ComponentType<never>; }' is not assignable to type 'ComponentType<{}> | { default: ComponentType<{}>; }'.
        Type '({ inline }: Props) => JSX.Element' is not assignable to type 'ComponentType<{}> | { default: ComponentType<{}>; }'.
          Type '({ inline }: Props) => JSX.Element' is not assignable to type 'FunctionComponent<{}>'.
            Types of parameters '__0' and 'props' are incompatible.
              Type '{ children?: ReactNode; }' has no properties in common with type 'Props'.ts(2345)

I can't figure out what the complaint is about, and I'd really appreciate any help!

Answer 1

dynamic is typed like that:

export default function dynamic<P = {}>(dynamicOptions: DynamicOptions<P> | Loader<P>, options?: DynamicOptions<P>): React.ComponentType<P>;

where P is props of the imported component

So, dynamic expects to get Loader<P> = LoaderComponent<P> = Promise<React.ComponentType<P>

You just need to tell him what the props are. Like this:

const Spinner = dynamic<{ inline?: boolean }>(
  () => import('components/ui/Spinner').then(mod => mod.Spinner)
)

or

import { Spinner as StaticSpinner } from 'components/ui/Spinner'

const Spinner = dynamic<React.ComponentProps<typeof StaticSpinner>>(
  () => import('components/ui/Spinner').then(mod => mod.Spinner)
)

or make Props as exported and then:

import { Props as SpinnerProps } from 'components/ui/Spinner'

const Spinner = dynamic<SpinnerProps>(
  () => import('components/ui/Spinner').then(mod => mod.Spinner)
)

Answer 2

@brc-dd is right, although small explanation why it works like that:

dynamic is typed like that:

export default function dynamic<P = {}>(dynamicOptions: DynamicOptions<P> | Loader<P>, options?: DynamicOptions<P>): React.ComponentType<P>;

So it expects you to return React.ComponentType<P> and it means:

type ComponentType<P = {}> = ComponentClass<P> | FunctionComponent<P>;

and FunctionComponent is:

interface FunctionComponent<P = {}> {
        (props: PropsWithChildren<P>, context?: any): ReactElement<any, any> | null;
        propTypes?: WeakValidationMap<P>;
        contextTypes?: ValidationMap<any>;
        defaultProps?: Partial<P>;
        displayName?: string;
    }

So you have to have props with children key. If you don't want to mess up your component interface and it's actually not accepting children then you can just type children?: never; in component Props interface.