Javascript - Getting "Cannot read properties of undefined (reading 'map')" Error. Even though the array is declared and imported

FrancisSales
November 8, 2023
161 views
1 vote
2 Answers

I am trying to map through an array and display names so I can eventually dynamically route to pages for each person. The array is coming back as undefined despite it being declared. So that is why .map is not working. But where am I going wrong here?

I have this code for an array
/lib/api

export async function getCastDetails() {
    const members = (
      {
        id: "1",
        name: "name one"
      },
      {
        id: "2",
        name: "name two"
      },
      {
        id: "3",
        name: "name three"
      }
    )
    return members;
  }

and I have this code to map through the array and display the names on a page

import { getCastDetails } from "@/lib/api";

export async function getStaticProps() {
    const castData = await getCastDetails();
    return {
        props: {
            castData,
        }
    }
}
const CastCarousel = ({ castData }) => {

    console.log(castData);
    return (
        <div>
            {castData.map(member => (
                <div
                    key={member.id}
                >
                    <a>{member.name}</a>
                </div>
            ))}
        </div>
    )
}

export default CastCarousel

I am then displaying on my index page

EDIT:
I believe I need to pass castData through my component on my index page, but I cannot figure out how to do that.

Here is what my index page looks like

import CastCarousel from "@/components/CastCarousel"

const Cast = () => {
    return (
        <main>
            <div className="flex flex-col justify-center items-center h-screen">
                <div>
                    <h1
                        className="text-6xl relative"
                    >Explore The Guys</h1>
                </div>
                <div className="">
                    <CastCarousel/>
                </div>
            </div>
        </main>
    )
}

export default Cast

Answers

- ElvisAdomnica
- November 8, 2023 at 12:08 am
- 0 votes
0
Arrays use [] and not (). I your case this function should be:
```
export async function getCastDetails() {
    const members = [
      {
        id: "1",
        name: "name one"
      },
      {
        id: "2",
        name: "name two"
      },
      {
        id: "3",
        name: "name three"
      }
    ]
    return members;
}
```
otherwise what is happening is that members is assigned the last object in that enumeration (the one with id 3) and that’s why you get the .map error because it is an object and not an array.
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- WebStylePress
- November 8, 2023 at 12:35 am
- 0 votes
0
The issue arises because the getCastDetails function is not returning an array but a single object due to a syntax error. The curly braces {} are used for creating objects, and when you want to return multiple objects in an array, you should enclose them in square brackets [].

Here is how you should modify your getCastDetails function to return an array of objects:
```
export async function getCastDetails() {
  const members = [
    {
      id: "1",
      name: "name one"
    },
    {
      id: "2",
      name: "name two"
    },
    {
      id: "3",
      name: "name three"
    }
  ];
  return members;
}
```
With this change, your castData should be an array, and the .map() function should work as expected.

Additionally, ensure that when you use CastCarousel on your index page, you pass castData as a prop:
```
import CastCarousel from "@/components/CastCarousel";
import { getStaticProps } from "@/components/CastCarousel";

// Call getStaticProps here or wherever appropriate to retrieve castData
const props = await getStaticProps();

const Cast = () => {
    return (
        <main>
            <div className="flex flex-col justify-center items-center h-screen">
                <div>
                    <h1 className="text-6xl relative">Explore The Guys</h1>
                </div>
                <div className="">
                    {/* Ensure to pass the retrieved castData as a prop */}
                    <CastCarousel castData={props.props.castData} />
                </div>
            </div>
        </main>
    )
}

export default Cast;
```
This will ensure that CastCarousel receives castData which is an array and can be mapped over to display the members’ names. Remember that getStaticProps is typically used in Next.js to fetch data at build time, so you need to ensure it’s called and the data is passed correctly to the component.
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