如何在映射函数中使用 async 和 await 进行顺序执行

Question

Hi for me async and await is quiet new .I have function call which requires await method so as a result i need to use async and await. I'm getting the values but they are not in order.

Below is my async and await map function

items.map(async (item) =>{
const itemx = await  
   Promise.all([w.getFileByServerRelativeUrl(item.FieldValuesAsText.FileRef).getItem()]);
  var likes = await Promise.all(itemx.getLikedByInformation());
  const comments = await Promise.all(itemx.comments.get());      
  articles[i].likecount = likes.likeCount
  articles[i].commentcount = comments.length
  articles[i].FileRef = item.FieldValuesAsText.FileRef
  newst.push(articles[i++])
  })

Any suggestion will really be helpful

Answer 1

You have to await promises of the map function to get results in order.

async function main() {
  const items = []; // Fill your items
  const articles = []; // Fill your articles

  // Async map function return promise for each item
  const promises = items.map(async (item, i) => {
    console.log(item.FieldValuesAsText.FileRef);
    const itemx = await Promise.all([
      w.getFileByServerRelativeUrl(item.FieldValuesAsText.FileRef).getItem()
    ]);

    console.log(item);
    var likes;
    likes = await Promise.all(itemx.getLikedByInformation());
    console.log("like " + likes.likeCount);
    const comments = await Promise.all(itemx.comments.get());
    console.log("Comments Count " + comments.length);

    // Create new object by appending articles[i],likes,comments
    return {
      ...articles[i],
      likecount: likes.likeCount,
      commentcount: comments.length,
      FileRef: item.FieldValuesAsText.FileRef
    };
  });

  // Here you have everything in order.
  const newst = await Promise.all(promises);
}

Each map item function runs asynchronously so there is no guarantee of order inside the map function, but you can return value from the map function which can be resolved to an ordered array by using await Promise.all() since the promise array returned by the map function is in the correct order.

Answer 2

try Promise.mapSeries for Sequential access with async await.

 async function main() {

 const items = []; // Fill your items
  const articles = []; // Fill your articles

  await Promise.mapseries( items, async (item, i) => {
    const itemx = await      

 Promise.all([w.getFileByServerRelativeUrl(item.FieldValuesAsText.FileRef).getItem()]);


  console.log(item);
  var likes
  likes = await Promise.all(itemx.getLikedByInformation());
 console.log("like " + likes.likeCount);
  const comments = await Promise.all(itemx.comments.get());
  console.log("Comments Count " + comments.length);


  //articles[i] = articles[i]+likes+comments
  articles[i].likecount = likes.likeCount
  articles[i].commentcount = comments.length
  articles[i].FileRef = item.FieldValuesAsText.FileRef
  console.log(articles[i])

  newst.push(articles[i++])
  console.log(newst)
  j++
  })