如何获得异步/等待 function 的结果？

Question

I would like to return an object from the the async / await function A to pass it to another function.

Currently what I get as a result is Promise{ <pending> }' or undefined.

function A:

const parseRss = data => data.forEach(rssLink => {
    const getFeed = async () => {
        try {
            const feed = await rssParser.parseURL(rssLink.rss);
            const emailContent = {
                emailBody: {
                    title: feed.title,
                    content: []
                }
            }

            feed.items.forEach(item => {
                feedObj.emailBody.content.push(`${item.title} : ${item.link}`)
            });
            return emailContent;
        } catch (e) {
            console.error(e);
        }
    };
    return (async () => {
        return await getFeed();
    })();
});

Function B:

    try {
        const data = await getDataWithRss();
        const emailData = await parseRss([{rss:'http://reddit.com/.rss'}]); // emailData is undefined
       return formatEmail(emailData);
    } catch (error) {
        console.log(error);
    }

How do I return emailContent from function A to use it in function B?

Thanks!

Answer 1

Since you made getFeed as async, no need another async. You are looping through, so return an array of promises. Once the you call use Promise.all to resolve. Since there could be multiple urls to fetch.

const parseRss = (data) =>
  data.map((rssLink) => {
    const getFeed = async () => {
      try {
        const feed = await rssParser.parseURL(rssLink.rss);
        const emailContent = {
          emailBody: {
            title: feed.title,
            content: [],
          },
        };

        feed.items.forEach((item) => {
          feedObj.emailBody.content.push(`${item.title} : ${item.link}`);
        });
        return emailContent;
      } catch (e) {
        console.error(e);
      }
    };
    return getFeed();
  });
  try {
    const data = await getDataWithRss();
    const emailData = await Promise.all(parseRss([{rss:'http://reddit.com/.rss'}])); // emailData is undefined
   return formatEmail(emailData);
} catch (error) {
    console.log(error);
}

Answer 2

await will not work inside a forEach loop. Use a for...in loop instead.

Answer 3

actually, getFeed() is not necessary inside inner scope, you can use async in map callback:

const parseRss = data => data.map(async rssLink => {
    const feed = await rssParser.parseURL(rssLink.rss);
    const emailContent = {
        emailBody: {
            title: feed.title,
            content: []
        }
    };

    feed.items.forEach(item => {
        feedObj.emailBody.content.push(`${item.title} : ${item.link}`)
    });

    return emailContent;
});