node.js - How to wait for a stream to finish piping? (Nodejs)

Question

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, 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?

question from:https://stackoverflow.com/questions/37837132/how-to-wait-for-a-stream-to-finish-piping-nodejs

Answer 1

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
  }
})