Infer Types leading to `props: never` #15913

lukebarton · 2020-08-05T18:28:12Z

Describe the bug

export const getServerSideProps = async ({ params }) => {
  return { 
    props: { foo: "bar" } 
  }
};

export const Page = (props: InferGetServerSidePropsType<typeof getServerSideProps>) => { ... }

causes props: never

however the following works fine:

export const getServerSideProps = async ({ params }: GetServerSidePropsContext) => {
  return { 
    props: { foo: "bar" } 
  }
};

export const Page = (props: InferGetServerSidePropsType<typeof getServerSideProps>) => { ... }

as does:

export const getServerSideProps = async (ctx) => {
  const params = ctx.params;
  return { 
    props: { foo: "bar" } 
  }
};

export const Page = (props: InferGetServerSidePropsType<typeof getServerSideProps>) => { ... }

The text was updated successfully, but these errors were encountered:

filipesmedeiros · 2020-08-07T01:03:39Z

Next only checks this:

export type InferGetServerSidePropsType<T> = T extends GetServerSideProps<
  infer P,
  any
>
  ? P
  : T extends (
      context?: GetServerSidePropsContext<any>
    ) => Promise<GetServerSidePropsResult<infer P>>
  ? P
  : never

So if neither the function is typed nor the argument, I think it has no way of knowing if the function is actually of type GetServerSideProps. I supose changing the above to something like:

export type InferGetServerSidePropsType<T> = T extends GetServerSideProps<
  infer P,
  any
>
  ? P
  : T extends (
      context?: any
    ) => Promise<GetServerSidePropsResult<infer P>>
  ? P
  : never

would make it infer your type, because the conditon would hold true?

lukebarton · 2020-08-25T22:04:53Z

I think you're right, however this one works, where the function isn't typed, and nor is the argument:

export const getServerSideProps = async (ctx) => {

JuanM04 · 2020-11-26T16:33:23Z

It also happens in cases like this:

export const getServerSideProps = async (ctx) => {
  const { userId } = ctx.params
  const user = await getUser(userId)

  if(user) {
    return {
      props: { user }
    }
  } else {
    return { notFound: true }
  }
};

tgallacher · 2021-01-13T17:59:11Z

This also doesn't work:

export const getServerSideProps: GetServerSideProps = async ({ params }) => {
  return { 
    props: { foo: "bar" } 
  }
};

export const Page = (props: InferGetServerSidePropsType<typeof getServerSideProps>) => { ... }

or

export const getServerSideProps: GetServerSideProps = async ({ params }: GetServerSidePropsContext) => {
  return { 
    props: { foo: "bar" } 
  }
};

export const Page = (props: InferGetServerSidePropsType<typeof getServerSideProps>) => { ... }

But removing the GetServerSideProps works:

export const getServerSideProps = async ({ params }: GetServerSidePropsContext) => {
  return { 
    props: { foo: "bar" } 
  }
};

export const Page = (props: InferGetServerSidePropsType<typeof getServerSideProps>) => { ... }

NextJS: v10.0.1

For me, the magic was to make sure the getServerSideProps function args are explicitly typed using the GetServerSidePropsContext type. Otherwise, the page props are inferred as any type, e.g. user: any.

GeeWee · 2021-02-17T12:52:21Z

I can confirm that @tgallacher bottom sample also works for me.

thisismydesign · 2021-05-17T13:43:37Z

This is a sneaky one, my string props were mistyped but that didn't even cause a problem with strict TS. It only was an issue when I had an object in the props and wanted to access a property.

nenadfilipovic · 2021-06-27T06:55:36Z

Here is my solution, key was to provide return type of getServerSideProps into GetServerSideProps type, here is example:
https://gist.github.com/nenadfilipovic/f2dd9cb903da93a7d14ed1de6b3493b1

varanakonda · 2021-07-12T15:01:09Z

Setting types like this works:

GetServerSideProps<{
    user: User
    posts: Post[]
}>

mkreuzmayr · 2021-08-17T12:44:43Z

I found out something interessing.
Type inference via InferGetServerSidePropsType<typeof getServerSideProps> seems to be working as long as I only return props.

return { 
  props: { 
    user: { 
      firstName,
      lastName 
    } 
  } 
};

If i additionally return a redirect or a notFound conditionally type inference stops working for me.

return {
  redirect: {
    destination: '',
    permanent: false,
  },
};

return {
  notFound: true
};

Setting types like this works:
GetServerSideProps<{
    user: User
    posts: Post[]
}>

This also works for me, but it would be more comfortable if it would work without the extra type specification.
If the type is created like this, you would not need to infer it, because you can directly use it in the component.

nenadfilipovic · 2021-08-17T12:51:41Z

It probably works in first case because return type is { [key: string]: any }
That is default type for props object

binajmen · 2021-08-18T09:10:12Z

Having the same issue. Is there a proper solution? Not quite sure which one to choose in all the previous suggestions.

mkreuzmayr · 2021-08-18T12:33:10Z

@binajmen

The easiest solution imo would be by adding a PageProps type to GetServerSideProps generic. If there is a fix that the type infer starts working without the extra type specification you are already set up. And having your PageProps typed out is not a bad thing either.

type PageProps = {
  user: { 
    firstName: string,
    lastName: string
  };
};

export const getServerSideProps: GetServerSideProps<PageProps> = async (ctx) => {
  return { 
    props: { 
      user: { 
        firstName,
        lastName 
      } 
    } 
  };
};

export const Page = ({ user }: InferGetServerSidePropsType<typeof getServerSideProps>) => { ... }

binajmen · 2021-08-18T15:33:03Z

Hi @mkreuzmayr

Thanks, sounds like an acceptable solution! However it doesn't work with next-firebase-auth and I can't figure out how to combine PageProps with it:

import type { GetServerSideProps, InferGetServerSidePropsType } from 'next'
import { AuthAction, useAuthUser, withAuthUser, withAuthUserTokenSSR } from 'next-firebase-auth'

function Page(props: InferGetServerSidePropsType<typeof getServerSideProps>) {
  const user = useAuthUser()

  return (
    <div>Message: {props.message} from {user.id}</div>
  )
}

export default withAuthUser<InferGetServerSidePropsType<typeof getServerSideProps>>({
  whenUnauthedBeforeInit: AuthAction.SHOW_LOADER,
  whenUnauthedAfterInit: AuthAction.REDIRECT_TO_LOGIN
})(Page)

export const getServerSideProps: GetServerSideProps<PageProps> = withAuthUserTokenSSR({
  whenUnauthed: AuthAction.REDIRECT_TO_LOGIN,
})(async () => {
  return { props: { message: "Hello" } }
})

TS error:

Type 'Promise<GetServerSidePropsResult<{ [key: string]: any; }>>' is not assignable to type 'GetServerSideProps<PageProps, ParsedUrlQuery>'.
  Type 'Promise<GetServerSidePropsResult<{ [key: string]: any; }>>' provides no match for the signature '(context: GetServerSidePropsContext<ParsedUrlQuery>): Promise<GetServerSidePropsResult<PageProps>>'.ts(2322)

KATT · 2021-09-02T13:29:11Z

I've found a workaround - first of all - something broke with 11.1.x as could use InferGetServerSidePropsType<typeof getServerSideProps> even with notFound using the below.

Here's my hacky implementation that I just wrote:

`utils/inferSSRProps.ts`

/* eslint-disable @typescript-eslint/no-explicit-any */

type GetSSRResult<TProps> =
  //
  { props: TProps } | { redirect: any } | { notFound: true };

type GetSSRFn<TProps extends any> = (args: any) => Promise<GetSSRResult<TProps>>;

export type inferSSRProps<TFn extends GetSSRFn<any>> = TFn extends GetSSRFn<infer TProps>
  ? NonNullable<TProps>
  : never;

`pages/somePage.tsx`

import { inferSSRProps } from '../utils/inferSSRProps'
import { GetServerSidePropsContext } from "next";
import prisma from "@lib/prisma";

export default MyPage(props: inferSSRProps<typeof getServerSideProps>) {
  // ...
}

export const getServerSideProps = async (context: GetServerSidePropsContext) => {
  const post = await prisma.post.findFirst({
    where: {
      username: (context.query.slug as string).toLowerCase(),
    },
    select: {
      id: true,
      // ...
    },
  });
  if (!post) {
    return {
      notFound: true,
    } as const; // <-- important, this needs to be `as const`
  }
  return {
    props: {
     post,
    },
  };
}

mkreuzmayr · 2021-09-03T10:48:26Z

Hey @KATT, thanks for your solution!

You do not need to cast { notFound: true } to const if you change your GetSSRResult notFound type to boolean.

`utils/inferSSRProps.ts`

/* eslint-disable @typescript-eslint/no-explicit-any */

type GetSSRResult<TProps> =
  { props: TProps } | { redirect: any } | { notFound: boolean }; // <-------

type GetSSRFn<TProps extends any> = (args: any) => Promise<GetSSRResult<TProps>>;

export type inferSSRProps<TFn extends GetSSRFn<any>> = TFn extends GetSSRFn<infer TProps>
  ? NonNullable<TProps>
  : never;

HaNdTriX · 2021-10-24T14:00:41Z

I solved the issue by publishing my own infer type:

works with notFound
works with redirect
universal works for getStaticProps as well as getServerSideProps
no dependencies

Install

npm install infer-next-props-type --save-dev

Usage:

getStaticProps

import InferNextPropsType from 'infer-next-props-type'

export function getStaticProps() {
   return {
     props: { foo: 'bar' }
   }
}

export default function Page(props: InferNextPropsType<typeof getStaticProps>) {
  return ...
}

getServerSideProps

import InferNextPropsType from 'infer-next-props-type'

export function getServerSideProps() {
   return {
     props: { foo: 'bar' }
   }
}

export default function Page(props: InferNextPropsType<typeof getServerSideProps>) {
  return ...
}

https://www.npmjs.com/package/infer-next-props-type

timneutkens · 2021-10-29T10:01:09Z

@HaNdTriX any reason for not updating the built-in type?

HaNdTriX · 2021-10-29T10:35:59Z

Because my type still has some edge cases to cover. Will deprecate the module as soon as we found the perfect working type and push the changes upstream.

balazsorban44 · 2021-12-01T02:35:46Z

Might be interesting microsoft/TypeScript#38511

Markyiptw · 2021-12-14T01:53:59Z

I found out something interessing. Type inference via InferGetServerSidePropsType<typeof getServerSideProps> seems to be working as long as I only return props.
return { 
  props: { 
    user: { 
      firstName,
      lastName 
    } 
  } 
};
If i additionally return a redirect or a notFound conditionally type inference stops working for me.
return {
  redirect: {
    destination: '',
    permanent: false,
  },
};
return {
  notFound: true
};
Setting types like this works:
GetServerSideProps<{
    user: User
    posts: Post[]
}>
This also works for me, but it would be more comfortable if it would work without the extra type specification. If the type is created like this, you would not need to infer it, because you can directly use it in the component.

returning an empty props in redirect worked for me:

return {
  redirect: {
    destination: '',
    permanent: false,
  },
  props: {}
}

aengl · 2022-02-03T17:55:15Z

Thanks @Markyiptw for the hint, that helped me a lot in figuring out what was going on.

The disadvantage of that solution is that the props will all become optional, so that may not always be ideal.

I slapped together this custom type that seems to do work well when using getServerSideProps that may return a redirect:

export type CustomInferGetServerSidePropsType<T> = T extends (
  context?: any
) => Promise<{ props: infer P }>
  ? P
  : T extends (context?: any) => Promise<GetServerSidePropsResult<infer P>>
  ? P
  : never;

I'm sharing this because the other types shared in this issue didn't quite work for my cases.

PabloLION · 2022-06-02T07:35:50Z

I found a best work around.
remove the : GetStaticProps from const getStaticProps = async () => {...}

Then the const SomePage: NextPage<InferGetStaticPropsType<typeof getStaticProps>>= ({/* inferred types */}){} can work correctly.

Problem was as said here #32434 (comment). So all after adding the : GetStaticProps , the return type of getStaticProps would be extended to { [key: string]: any; } by TS because it includes the original type of {'foo': string}.

flybayer · 2022-08-27T17:34:22Z

Looks like this will hopefully be solved with Typescript 4.9!

https://twitter.com/leeerob/status/1563540593003106306

andparsons · 2022-08-27T23:43:17Z

I was playing around with the new satisfies keyword and I can certainly see it helping.

We’ll still need to cast the notFound and redirects returns as consts.

I’m also of the opinion that we should expect props to be able to return null unless a type guard is in place, which I’ve also included in the below example.

Link to ts playground

HaNdTriX · 2022-09-20T09:14:35Z

I have created a PR to solve this issue^^

@timneutkens

## Problem Currently the Next.js infer utility (`InferGetServerSidePropsType` and `InferGetStaticPropsType`) types can lead to a wrong inferred types (`never`). This happens if these functions return something different than: `{props: {}}`. **Example:** `getServerSideProps` ```typescript export async function getServerSideProps({ query }: GetServerSidePropsContext) { if (query.foo) { return { notFound: true, } } return { props: { foo: "bar" }, } } type PageProps = InferGetServerSidePropsType<typeof getServerSideProps> // => type PageProps = never ``` **Example:** `getStaticProps` ```typescript import type { InferGetStaticPropsType, GetStaticPropsContext } from 'next' export async function getStaticProps(context: GetStaticPropsContext) { if (context.params?.bar) { return { notFound: true, } } return { props: { foo: 'bar', }, } } type PageProps = InferGetStaticPropsType<typeof getStaticProps> // => type PageProps = never ``` This is because the first infer condition of the utility type is not satified leading to a never result. ```typescript export type InferGetServerSidePropsType<T> = T extends GetServerSideProps< infer P, // <- NOT SATISFIED any > ? P : T extends ( context?: GetServerSidePropsContext<any> ) => Promise<GetServerSidePropsResult<infer P>> ? P : never // <- NOT SATISFIED ``` ## Solution I have experimented with different solutions ending with a much simpler type, that is faster to execute, easier to read and universally usable for both prop variations. ```typescript /** * Flow: * - Make sure getStaticProps is a function * - Get its return type * - Extract the one that contains {props: any} * - Return the props */ export type InferGetStaticPropsType<T extends (args: any) => any> = Extract< Awaited<ReturnType<T>>, { props: any } >['props'] ``` ## Bug - [x] Related issues: fixes #36615, #15913, https://twitter.com/leeerob/status/1563540593003106306 - [x] Type tests added ## Future thoughts Since `InferGetStaticPropsType` and `InferGetServerSidePropsType` are now the same, it's api could be merged into one utility type (e.g: InferNextProps). I recommend doing this in a different PR. ## Additional info I have tested this approach using the following [external package](https://www.npmjs.com/package/infer-next-props-type) (@timneutkens sorry for the late PR). Since about 12 Month I haven't received any negative feedback (issues) regarding this approach. Co-authored-by: JJ Kasper <jj@jjsweb.site>

HaNdTriX · 2022-10-03T11:09:28Z

This issue has been fixed by #40635

ijjk · 2022-10-03T17:47:01Z

Closing per above

github-actions · 2022-11-03T00:24:32Z

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.

lukebarton changed the title ~~Infer Types don't work brilliantly~~ Infer Types leading to props: never Aug 5, 2020

Timer added kind: bug good first issue Easy to fix issues, good for newcomers labels Aug 5, 2020

Timer added this to the backlog milestone Sep 7, 2020

zomars mentioned this issue Aug 26, 2021

UX: Allows going back to dashboard when cancelling from there calcom/cal.com#527

Closed

ijjk mentioned this issue Aug 26, 2021

TS getServerSideProps hinting disappears when using both type and infer #28543

Closed

kmjennison mentioned this issue Aug 27, 2021

NextJS Infer type lead to props: never gladly-team/next-firebase-auth#279

Closed

ijjk mentioned this issue Sep 18, 2021

InferGetStaticPropsType not working as expected #28638

Closed

timneutkens mentioned this issue Oct 31, 2021

InferGetStaticPropsType does not infer props when GetStaticProps is used #29963

Closed

timneutkens added the TypeScript Related to types with Next.js. label Nov 17, 2021

timfee mentioned this issue Dec 13, 2021

InferGetStaticPropsType always returns { [key: string]: any; } #32434

Closed

bautistaaa mentioned this issue Jun 15, 2022

fix: static props inference trpc/examples-kitchen-sink#62

Closed

HaNdTriX mentioned this issue Sep 17, 2022

fix: InferGetServerSidePropsType and InferGetStaticPropsType #40635

Merged

2 tasks

ijjk closed this as completed Oct 3, 2022

github-actions bot locked as resolved and limited conversation to collaborators Nov 3, 2022

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Infer Types leading to `props: never` #15913

Infer Types leading to `props: never` #15913

lukebarton commented Aug 5, 2020 •

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lukebarton commented Aug 25, 2020

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tgallacher commented Jan 13, 2021

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KATT commented Sep 2, 2021

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timneutkens commented Oct 29, 2021

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github-actions bot commented Nov 3, 2022

Infer Types leading to props: never #15913

Infer Types leading to props: never #15913

Comments

lukebarton commented Aug 5, 2020 • edited Loading

Describe the bug

filipesmedeiros commented Aug 7, 2020 • edited Loading

lukebarton commented Aug 25, 2020

JuanM04 commented Nov 26, 2020

tgallacher commented Jan 13, 2021

GeeWee commented Feb 17, 2021

thisismydesign commented May 17, 2021

nenadfilipovic commented Jun 27, 2021

varanakonda commented Jul 12, 2021

mkreuzmayr commented Aug 17, 2021 • edited Loading

nenadfilipovic commented Aug 17, 2021 • edited Loading

binajmen commented Aug 18, 2021

mkreuzmayr commented Aug 18, 2021

binajmen commented Aug 18, 2021 • edited Loading

KATT commented Sep 2, 2021

utils/inferSSRProps.ts

pages/somePage.tsx

mkreuzmayr commented Sep 3, 2021

utils/inferSSRProps.ts

HaNdTriX commented Oct 24, 2021 • edited Loading

Install

Usage:

getStaticProps

getServerSideProps

timneutkens commented Oct 29, 2021

HaNdTriX commented Oct 29, 2021

balazsorban44 commented Dec 1, 2021

Markyiptw commented Dec 14, 2021

aengl commented Feb 3, 2022 • edited Loading

PabloLION commented Jun 2, 2022

flybayer commented Aug 27, 2022

andparsons commented Aug 27, 2022

HaNdTriX commented Sep 20, 2022

HaNdTriX commented Oct 3, 2022

ijjk commented Oct 3, 2022

github-actions bot commented Nov 3, 2022

Infer Types leading to `props: never` #15913

Infer Types leading to `props: never` #15913

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binajmen commented Aug 18, 2021 •

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`utils/inferSSRProps.ts`

`pages/somePage.tsx`

`utils/inferSSRProps.ts`

HaNdTriX commented Oct 24, 2021 •

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