"Encountering a build failure in Next.js when using getStaticProps because a parameter is returning undefined

Question

"Encountering a build failure in Next.js when using getStaticProps because a parameter is returning undefined

An unusual error has recently surfaced, causing our builds to fail,

Located within the pages directory is a post/[id].tsx file that utilizes getStaticProps and getStaticPaths

-- props

export const getStaticProps: GetStaticProps = async ({ params }) => {
  const res: Response = await fetch(`${baseUrl}/api/products/${params.id}`);

  const data: Product[] = await res.json();

  return {
    props: {
      data,
    },
  };
};

-- paths

export const getStaticPaths: GetStaticPaths = async () => {
  const res: Response = await fetch(`${baseUrl}/api/products`);
  const { data } = await res.json();

  const paths = data.map((product: Product) => ({
    params: { id: product.id.toString() },
  }));
  return { paths, fallback: "blocking" };
};

When running npm run dev locally, everything functions as intended. However, during npm run build, an error surfaces:

Type error: Object is possibly 'undefined'.

specifically within the getStaticProps function

> 12 |   const res: Response = await fetch(`${baseUrl}/api/products/${params.id}`);
                                                                      ^

The perplexing aspect is that the current build deployed on vercel employs identical code to construct this page with no recent modifications. Why are builds suddenly failing now?

typescript next.js

Answer 1

Answer №1

Building on @Pranta's previous answer, I have made some tweaks to address the issue at hand. While Pranta's solution is effective in many ways, there could still be a warning generated by Typescript regarding the id variable declaration, although this may not impact the build process. It is important to understand that this warning arises because Next.js defines the type of the params object as ParsedUrlQuery | undefined.

To eliminate this warning completely, one approach is to assert the type of the params object as ParsedUrlQuery, as demonstrated below:

// The import should happen automatically in VSCode, but if it doesn't
import { ParsedUrlQuery } from 'querystring';

const id = (params as ParsedUrlQuery).id;
const res: Response = await fetch(`${baseUrl}/api/products/${id}`);

While this method works, a more optimal solution would involve checking if the params object is defined before making the API call within the getStaticProps function. This proactive approach can help prevent potential issues down the line. Here's how you can implement it:

if (params) {
  const id = params.id;
  const res: Response = await fetch(`${baseUrl}/api/products/${id}`);
}

In addition, we can enhance the code further by ensuring that a valid value for the id path parameter is obtained from the getStaticPaths function with an extra check:

if (params && params.id) {
  const res: Response = await fetch(`${baseUrl}/api/products/${params.id}`);
}

Finally, since the getStaticProps function requires a return value, it's necessary to specify a default return value that aligns with the expected structure, as illustrated below.

export const getStaticProps: GetStaticProps = async ({ params }) => {
  if (params && params.id) {
    const res: Response = await fetch(`${baseUrl}/api/products/${params.id}`);
    const data: Product[] = await res.json();
    return {
      props: { data },
    };
  }

  // In case of an error, customize the return value based on your requirements.
  return {
    props: { error: true },
  };
};

Answer 2

Building on @Pranta's previous answer, I have made some tweaks to address the issue at hand. While Pranta's solution is effective in many ways, there could still be a warning generated by Typescript regarding the id variable declaration, although this may not impact the build process. It is important to understand that this warning arises because Next.js defines the type of the params object as ParsedUrlQuery | undefined.

To eliminate this warning completely, one approach is to assert the type of the params object as ParsedUrlQuery, as demonstrated below:

// The import should happen automatically in VSCode, but if it doesn't
import { ParsedUrlQuery } from 'querystring';

const id = (params as ParsedUrlQuery).id;
const res: Response = await fetch(`${baseUrl}/api/products/${id}`);

While this method works, a more optimal solution would involve checking if the params object is defined before making the API call within the getStaticProps function. This proactive approach can help prevent potential issues down the line. Here's how you can implement it:

if (params) {
  const id = params.id;
  const res: Response = await fetch(`${baseUrl}/api/products/${id}`);
}

In addition, we can enhance the code further by ensuring that a valid value for the id path parameter is obtained from the getStaticPaths function with an extra check:

if (params && params.id) {
  const res: Response = await fetch(`${baseUrl}/api/products/${params.id}`);
}

Finally, since the getStaticProps function requires a return value, it's necessary to specify a default return value that aligns with the expected structure, as illustrated below.

export const getStaticProps: GetStaticProps = async ({ params }) => {
  if (params && params.id) {
    const res: Response = await fetch(`${baseUrl}/api/products/${params.id}`);
    const data: Product[] = await res.json();
    return {
      props: { data },
    };
  }

  // In case of an error, customize the return value based on your requirements.
  return {
    props: { error: true },
  };
};

Answer 3

Answer №2

One issue arises in this situation as next.js is performing a type check and typescript assumes that your params could potentially be undefined in this case. Simply inform typescript that this assumption is incorrect.

  const id = params.id!
  const response: Response = await fetch(`${baseUrl}/api/products/${id}`);

Following these adjustments, everything should function as expected.

Answer 4

One issue arises in this situation as next.js is performing a type check and typescript assumes that your params could potentially be undefined in this case. Simply inform typescript that this assumption is incorrect.

  const id = params.id!
  const response: Response = await fetch(`${baseUrl}/api/products/${id}`);

Following these adjustments, everything should function as expected.

"Encountering a build failure in Next.js when using getStaticProps because a parameter is returning undefined

Answer №1

Answer №2

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