Axios 请求失败并触发无法读取未定义的属性“地图”

Question

I am working on a blog post project. I have a method renderPostList() that renders a list of posts. I am using the .map function on the array. When I access /post/list route, the Axios request is not firing and there is nothing in the redux store. Therefore, undefined.map() is called that causes this error. The console.log(this.props.posts) is returning an empty array due to request failure. Even if I write a conditional of "if(this.props.posts)" the method still executes the .map on the undefined array. Is there a way to make this work correctly? I need the data to be passed before .map executes. And why the conditional is not working?

componentDidMount() {
    this.props.getPosts();
    this.setState({
      items: this.props.posts.filter(function (post) {
        return post.isRelated === false;
      }).length,
    });
  }

renderPostList() {
    if (this.props.posts) { //not working conditional
      console.log(this.props.posts);
      let filtered_posts = this.props.posts.filter(function (post) {
        return post.isRelated === false;
      });
      var postChunks = this.chunkArray(filtered_posts, 3);
        return postChunks[this.state.activePage - 1].map(
          ({ title, meta_info, timestamp, img, id }) => {
            return (
              <div className="item" key={id}>
                <Post
                  title={title}
                  meta_info={meta_info}
                  timestamp={timestamp}
                  img={img}
                />
              </div>
            );
          }
        );
    }
    return null;
  }

const mapStateToProps = (state) => {
  return { posts: state.posts };
};

export default connect(mapStateToProps, { getPosts })(News);

Action

export const getPosts = () => async (dispatch) => {
  const response = await api.get("post/list");
  dispatch({ type: "GET_POSTS", payload: response.data });
};

Reducer

export default (state = [], action) => {
    switch (action.type) {
      case 'GET_POSTS':
        return action.payload;
      default:
        return state;
    }
  };

Axios instance

export default axios.create({
  baseURL: dev_url,
  headers: {
    "X-Requested-With": "XMLHttpRequest",
  },
});

I will appreciate any feedback on this code. Thanks!

Answer 1

The condition will pass cause javascript script returns true for an empty array. the condition should be

if(this.props.post.length)

if the array length is zero the condition will not pass.