How can I send 'blocking' parameter to getStaticPaths function in Next.js using TypeScript?

Question

How can I send 'blocking' parameter to getStaticPaths function in Next.js using TypeScript?

Whenever I try to use fallback: 'blocking', in my Next.js page, TypeScript throws an error. I am using the latest 12.2.0 version of Next.js. What could be causing this issue?

Type '() => Promise<{ paths: any; fallback: string; }>' is not assignable to type 'GetStaticPaths<ParsedUrlQuery>'.
  Type 'Promise<{ paths: any; fallback: string; }>' is not assignable to type 'GetStaticPathsResult<ParsedUrlQuery> | Promise<GetStaticPathsResult<ParsedUrlQuery>>'.
    Type 'Promise<{ paths: any; fallback: string; }>' is not assignable to type 'Promise<GetStaticPathsResult<ParsedUrlQuery>>'.
      Type '{ paths: any; fallback: string; }' is not assignable to type 'GetStaticPathsResult<ParsedUrlQuery>'.
        Types of property 'fallback' are incompatible.
          Type 'string' is not assignable to type 'boolean | "blocking"'.

Here's the code snippet:

export const getStaticPaths: GetStaticPaths = async () => {
// ...
    const paths = res.data.map((organizationAndPostId: string) => ({
        params: {
            organizationShortId: organizationAndPostId[0],
            postId: organizationAndPostId[1],
            tempUserShortId: organizationAndPostId[2],
            imgId: organizationAndPostId[3],
        },
    }))

    let ret = {
        paths,
        fallback: 'blocking',
    }
    return ret
}

I suspect the issue could be related to the quotes used in the code. Despite manually changing it to ', VSCode keeps converting it automatically.

typescript next.js

Answer 1

Answer №1

The reason for the type error is due to how TypeScript interprets the ret object. It assumes that the fallback property should be of type string instead of the specific string value 'blocking'. This causes a mismatch with the expected type for GetStaticPaths.

const obj: { 
    paths: { 
        params: { category: string; }; 
    }[];
    fallback: string; // The expected type for `fallback` by `GetStaticPaths`
}

To resolve this issue, you have two options:

You can simply return the object directly without using an intermediate variable.

export const getStaticPaths: GetStaticPaths = async () => {
    //...

    return {
        paths,
        fallback: 'blocking'
    }
}

Alternatively, you can explicitly cast the fallback value as a const to enforce the specific string type.

export const getStaticPaths: GetStaticPaths = async () => {
    //...

    let ret = {
        paths,
        fallback: 'blocking' as const,
    }
    return ret
}

Answer 2

The reason for the type error is due to how TypeScript interprets the ret object. It assumes that the fallback property should be of type string instead of the specific string value 'blocking'. This causes a mismatch with the expected type for GetStaticPaths.

const obj: { 
    paths: { 
        params: { category: string; }; 
    }[];
    fallback: string; // The expected type for `fallback` by `GetStaticPaths`
}

To resolve this issue, you have two options:

You can simply return the object directly without using an intermediate variable.

export const getStaticPaths: GetStaticPaths = async () => {
    //...

    return {
        paths,
        fallback: 'blocking'
    }
}

Alternatively, you can explicitly cast the fallback value as a const to enforce the specific string type.

export const getStaticPaths: GetStaticPaths = async () => {
    //...

    let ret = {
        paths,
        fallback: 'blocking' as const,
    }
    return ret
}

How can I send 'blocking' parameter to getStaticPaths function in Next.js using TypeScript?

Answer №1

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