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Next.js, getStaticProps not working. TypeError: Cannot read properties of undefined (reading 'map')

I created a project starting from create-next-app. Inside the Blog.js page I tried to fetch from https://jsonplaceholder.typicode.com/posts using the getStaticProps() function.

I used the guide https://nextjs.org/docs/basic-features/data-fetching/get-static-props#using-getstaticprops-to-fetch-data-from-a-cms. Once everything is implemented, I open the page in the browser and it tells me

Server Error
TypeError: Cannot read properties of undefined (reading 'map')

Here is the code

function Blog({ posts }) {
  return (
    <ul>
      {posts.map((post) => (
        <li>{post.title}</li>
      ))}
    </ul>
  )
}

export async function getStaticProps() {
  const res = await fetch('https://jsonplaceholder.typicode.com/posts')
  const posts = await res.json()

  return {
    props: {
      posts,
    },
  }
}

export default Blog
about 4 years ago · Juan Pablo Isaza
1 answers
Answer question

0

you are writting the function inside of the component you want to render. The only situation you are going to do this is when you are making dynamic URLs based on some parameter, in that case you will use getStaticProps and getStaticPages mixed.

try to do something like this:

  1. Writte your Blog component in a file (Blog.tsx/jsx):

function Blog({ posts }) {
  return (
    <ul>
      {posts.map((post) => (
        <li key={post.id}>{post.title}</li>
      ))}
    </ul>
  )
}

export default Blog

  1. Go to the page where you will render this component (it could be an index.tsx/jsx for instance)
import type { NextPage } from "next";
import Blog from 'wherever it is'

const Home: NextPage = ({posts}) => {
  return (
    <>
          <Blog posts={posts}/>    
    </>
  );
};

export async function getStaticProps() {
  const res = await fetch('https://jsonplaceholder.typicode.com/posts')
  const posts = await res.json()
  
  return {
    props: {
      posts,
    },
  }
}


export default Home;

Ps.: when you are using map, never forget the key property ;) Hope it could help ya, hugs from Brazil.

about 4 years ago · Juan Pablo Isaza Report
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