Exploring NextJS with Typescript to utilize the getStaticProps method

Question

Exploring NextJS with Typescript to utilize the getStaticProps method

I'm currently enrolled in a NextJS course and I am interested in using Typescript. While browsing through a GitHub discussion forum, I came across an issue that I don't quite understand. The first function provided below seems to be throwing an error, while the second one is not.

export async function getStaticProps(): GetStaticProps {
    return {
        props: {
            example:  ""
        }
    }
}

The error message for the aforementioned function is as follows:

The return type of an async function or method must be the global Promise type. Did you mean to write 'Promise<GetStaticProps<{ [key: string]: any; }, ParsedUrlQuery, PreviewData>>'?

export const getStaticProps: GetStaticProps = async () => {
    return {
        props: {
            example: ""
        }
    }
};

Interestingly, the error does not occur for the second function. This discrepancy has left me puzzled. Even though both functions have similar definitions, with one being a regular function and the other an arrow function, why does only one trigger an error?

If anyone could shed some light on how I can resolve this issue with the appropriate TypeScript types in the first function, it would be greatly appreciated. I'd like to better understand what's causing this disparity.

javascript typescript function next.js getstaticprops

Answer 1

Answer №1

When defining functions, it's important to note where you specify the type in TypeScript. The first function's type specification refers to the return type of the function, while the second function's type specification is for the type of the function itself.

For instance, consider these two functions which are essentially of the same type, but the location of the type specification is crucial.

const hi: () => string = () => {
    return "a"
}

const hi2 = (): string => {
    return "a"
}

In response to your question about async functions, it's worth noting that all async functions must ultimately return a Promise. Your first function likely resulted in an error because it returned GetStaticProps, which is not a promise. To resolve this, ensure that you define the return type as Promise<GetStaticProps>.

Answer 2

When defining functions, it's important to note where you specify the type in TypeScript. The first function's type specification refers to the return type of the function, while the second function's type specification is for the type of the function itself.

For instance, consider these two functions which are essentially of the same type, but the location of the type specification is crucial.

const hi: () => string = () => {
    return "a"
}

const hi2 = (): string => {
    return "a"
}

In response to your question about async functions, it's worth noting that all async functions must ultimately return a Promise. Your first function likely resulted in an error because it returned GetStaticProps, which is not a promise. To resolve this, ensure that you define the return type as Promise<GetStaticProps>.

Exploring NextJS with Typescript to utilize the getStaticProps method

Answer №1

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