Error: Element type is invalid: expected a string (for built-in components) or a class/function

Question

• I am trying to learn react redux api call
• so I took an example and implemented in stackblitz but I am getting the below error when I select some channel and hit top news button
• can you tell me how to fix it
• providing my code and stackblitz below https://medium.com/@lavitr01051977/basic-react-redux-app-with-async-call-to-api-e478e6e0c48b

https://stackblitz.com/edit/react-redux-realworld-j95tpu?file=actions/index.js

code
export function fetchPosts(channel) {
  return function (dispatch) {
    dispatch(requestPosts());
    return fetch(`https://newsapi.org/v1/articles?source=${channel}&apiKey=${MY_API_KEY}`)
      .then(response => response.json(),
      error => console.log('An error occurred.', error),
    )
      .then((json) => {
        dispatch(receivedPosts(json));
      }, );
  };
}

error

VM1672:37 Warning: React.createElement: type is invalid -- expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in. Check the render method of `TopNews`.
    in TopNews (created by Connect(TopNews))
    in Connect(TopNews) (created by App)
    in div (created by App)
    in App
    in Provider


Uncaught (in promise) Error: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in. Check the render method of `TopNews`.
    at invariant (invariant.js:42)
    at instantiateReactComponent (instantiateReactComponent.js:74)
    at instantiateChild (ReactChildReconciler.js:44)
    at eval (ReactChildReconciler.js:71)
    at traverseAllChildrenImpl (traverseAllChildren.js:77)
    at traverseAllChildren (traverseAllChildren.js:172)
    at Object.instantiateChildren (ReactChildReconciler.js:70)
    at ReactDOMComponent._reconcilerInstantiateChildren (ReactMultiChild.js:185)
    at ReactDOMComponent.mountChildren (ReactMultiChild.js:224)
    at ReactDOMComponent._createInitialChildren (ReactDOMComponent.js:703)

Answer 1

The actual problem is an import/export syntax issue. I'll walk you through how to find it.

The problem's real location is shown by the component stack trace:

Warning: React.createElement: type is invalid -- expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in. Check the render method of `TopNews`.
    in TopNews (created by Connect(TopNews))
    in Connect(TopNews) (created by App)
    in div (created by App)
    in App
    in Provider

If we look in TopNews.js, it only renders <h3>, <div>, and <NewsItem>. h3 and div are just basic tags, so it's probably NewsItem that's the problem.

At the top of TopNews.js, you have:

import { NewsItem } from '../components/NewsItem';

However, in NewsItem.js, you have:

export default NewsItem ;

So, you're doing a default export, but a named import, and so NewsItem is undefined in TopNews.js.

Try changing it to be import NewsItem from "../components/NewsItem" and it should work.