Question

我有一个生命周期方法componentDidMount，它调用一个递归异步方法，并且我希望递归函数在获取所有数据后返回一个Promise。

def counter(z, c=0):
    if not z: return c
    return counter(z[1:], c+1)

并且被调用的函数是

  async componentDidMount() {
    let response = await fetch(`${STORY_URL}${this.props.match.params.id}.json`);
    let result = await response.json();

    totalComments = result.descendants;

    await this.fetchComments(result.kids, MARGIN);

    this.setState({
      by: result.by,
      time: calculateTimeDifference(result.time)
    });
  }

，但是resolve方法不会返回到setState之前的componentDidMount。我通过控制台日志检查。我不知道我在做什么错

Answer 1

您使事情变得过于复杂。使用Promise.all：

 async fetchComments(comments, margin) {
   // Collect all the results here, otgerwise we would have to flatMap the promises which is more complicated
   const result = [];

   // Make sure that all comments were processed before returning
   await Promise.all( comments.map(async commentId => {
    const response = await fetch(`${STORY_URL}${commentId}.json`);
    const { kids, by } = await response.json();

    if(kids) {
       // Get all children and append them to the results, right after the children
       const children = await fetchComments(kids, margin * 2);
       result.push({ by, margin }, ...children);
    } else {
       // Otherwise just append this node
      result.push({ by, margin });    
    }   
  }));

  return result;
}

如果顺序很重要，则必须将Promise.all的结果展平：

  async fetchComments(comments, margin) {
    const result = await Promise.all(comments.map( async commentID => {
      const response = await fetch(STORY_URL + commentID + ".json");
      const { by, kids } = await response.json();

      const result = [{ by, margin }];
      if(kids) result.push(... await fetchComments(kids, margin * 2));

      return result;
   }));

   // Flatten the results
   return [].concat(...result);
 }

如何在异步功能中解决承诺？

1 个答案: