javascript - Objects are not valid as a React child (found: [object Promise])

Question

I am trying to render a list of posts by mapping through an array. I've done this many times before but for some reason

renderPosts = async () => {
    try {
      let res = await axios.get('/posts');
      let posts = res.data;
      return  posts.map((post, i) => {
        return (
          <li key={i} className="list-group-item">{post.text}</li>
        );
      });
    } catch (err) {
      console.log(err);
    }
  }

  render () {
    return (
      <div>
        <ul className="list-group list-group-flush">
          {this.renderPosts()}
        </ul>
      </div>
    );
  }

All I get is:

Uncaught Error: Objects are not valid as a React child (found: [object Promise]). If you meant to render a collection of children, use an array instead.

I've checked the data returned from renderPosts and it is an array with the correct values and no promises. What's going on here?

Answer 1

this.renderPosts() will return a Promise not the actual data, and AFAIK Reactjs will not resolve Promises implicitly in render.

You need to do it like this

componentDidMount() {
  this.renderPosts();
}

renderPosts = async() => {
  try {
    const res = await axios.get('/posts');
    const posts = res.data;

    // this will re render the view with new data
    this.setState({
      Posts: posts
    });
  } catch (err) {
    console.log(err);
  }
}

render() {
  const posts = this.state.Posts?.map((post, i) => (
    <li key={i} className="list-group-item">{post.text}</li>
  ));

  return (
    <div>
      <ul className="list-group list-group-flush">
        {posts}
      </ul>
    </div>
  );
}