如何等待流完成管道?(节点) [英] How to wait for a stream to finish piping? (Nodejs)

问题描述

我有一个 for 循环的 promise 数组，所以我使用 Promise.all 来遍历它们，然后调用 then.

I have a for loop array of promises, so I used Promise.all to go through them and called then afterwards.

let promises = [];
promises.push(promise1);
promises.push(promise2);
promises.push(promise3);

Promise.all(promises).then((responses) => {
  for (let i = 0; i < promises.length; i++) {
    if (promise.property === something) {
      //do something
    } else {
      let file = fs.createWriteStream('./hello.pdf');
      let stream = responses[i].pipe(file);
      /*
         I WANT THE PIPING AND THE FOLLOWING CODE 
         TO RUN BEFORE NEXT ITERATION OF FOR LOOP
      */
      stream.on('finish', () => {
        //extract the text out of the pdf
        extract(filePath, {splitPages: false}, (err, text) => {
        if (err) {
          console.log(err);
        } else {
          arrayOfDocuments[i].text_contents = text;
        }
      });
    });    
  }
}

promise1、promise2 和 promise3 是一些 http 请求，如果其中一个是应用程序/pdf，那么我将其写入流并从中解析文本.但是此代码在从 pdf 中解析测试之前运行下一次迭代.有没有办法让代码等到流的管道和提取完成后再进行下一次迭代?

promise1, promise2, and promise3 are some http requests, and if one of them is an application/pdf, then I write it to a stream and parse the text out of it. But this code runs the next iteration before parsing the test out of the pdf. Is there a way to make the code wait until the piping to the stream and extracting are finished before moving on to the next iteration?

推荐答案

如果没有 async/await，那就太糟糕了.使用异步/等待，只需执行以下操作:

Without async/await, it's quite nasty. With async/await, just do this:

Promise.all(promises).then(async (responses) => {
  for (...) {
    await new Promise(fulfill => stream.on("finish", fulfill));
    //extract the text out of the PDF
  }
})

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