使用回调循环 function 并等待结果

Question

我了解 await、async 和 Promises 的基本概念。 我尝试了很多，但无法获得预期的结果。 为此，我向你们寻求帮助。 提前谢谢。

我踢掉了所有不必要的代码行，您可以快速看到我想要做什么。

app.post('/create',  (req,res) => {

  var dataArray = [] 

  req.body.array.forEach((ele) => {

  let blobAdress = ele.link.split('/')[0];
  let extracted = ele.extracted
  let blob = `${blobAdress}/extracted-${extracted}.json`;
  const container =  'test';

  //SHOULD BE EXECUTED FOR EACH ELEMENT OF FOR LOOP  
 
  api.getTextFromBlob(container, blob,  (response, error) => {
   if (error){console.log("Error",error)}
     let jsonResponse = JSON.parse(response);
     console.log(jsonResponse)
     dataArray.push(jsonResponse) // I WANT ALL DATA FROM THE CB IN ONE ARRAY BUNDLED
     })
  })

// RUN THIS PART AFTER FOR LOOP HAS BEEN EXECUTED PROPER

console.log(dataArray) // !ASYNC JS --> DATA ARRAY IS EMPTY BECAUSE datArray IS CONSOLE.LOG BEFORE api.getText EXECTUED
})    

Answer 1

您需要首先将回调 function 包装到Promise object 中：

var getTextFromBlobAsPromise = (container, blob) => new Promise((resolve, reject) => {
    api.getTextFromBlob(container, blob, (response, error) => {
        if (error) {
            console.log("Error", error)
            return reject(error); // depends on business
        }
        let jsonResponse = JSON.parse(response);
        console.log(jsonResponse)
        resolve(jsonResponse);
    })
})

然后你可以等待，直到所有的承诺都将使用Promise.all function 解决：

app.post('/create', (req, res) => {

    var promises = [];
    req.body.array.forEach((ele) => {
        let blobAdress = ele.link.split('/')[0];
        let extracted = ele.extracted
        let blob = `${blobAdress}/extracted-${extracted}.json`;
        const container = 'test';

        //SHOULD BE EXECUTED FOR EACH ELEMENT OF FOR LOOP
        promises.push(getTextFromBlobAsPromise(container, blob))   ;
    })

    // RUN THIS PART AFTER FOR LOOP HAS BEEN EXECUTED PROPER
    Promise.all(promises).then(dataArray => {
        console.log(dataArray) // !ASYNC JS --> DATA ARRAY IS EMPTY BECAUSE datArray IS CONSOLE.LOG BEFORE api.getText EXECTUED
    })
})