How do I make multiple sequential calls with axios?

Question

I'm getting a headache from trying to come up with a solution, and I hope that someone here can solve my problem.

I am trying to create a program that will do a loop for a number of audio files, using NodeJS:

1. Access audio file from source.
2. Send audio file to outside API for treatment (this part is already handled).
3. Obtain the answer to the audio file treatment
4. Display the answer

The API cannot work on 2 or more audios at the same time because it mixes them up and returns incorrect results, so the audio list has to be handled sequentially (so, it does steps 1-5 for audio_1, then steps 1-5 for audio_2, etcetera).

I can do the loop just fine, but due to how Promises work, what the program actually does is this:

1. Do step 1 for audio_1.
2. Get a Promise to do step 2 for audio_1.
3. Do step 1 for audio_2.
4. Get a Promise to do step 2 for audio_2...
5. Once it gets all the Promises, it listens in until all the the Promises are resolved.

And this messes things up due to the above mentioned problem.

Here's the code I have right now:

async function myFunction(client){
  ...
  const fileC = database()
  const vars = {"variable":"my_variable"}
  const url = "my_url"

  let result
  await fileC.find({}).forEach(f=>fileList.push(f))
  for (const f of fileList){
    await https.get(f.file_location,function(res){
      let form = new FormData()
      Object.keys(vars).forEach(key=>form.append(key,vars[key]))
      form.append("file",res,f.file_name)
      axios.post(url,form,{headers:form.getHeaders(),maxBodyLength:Infinity}).then((response)=>{
        console.log(response.data.val)
      })
    })
  }
}

My only obstacle is ensuring that the for loop will not move to one cycle until the previous one has finished - once I get that, then my full program should work.

Any ideas?

EDIT: modified a bunch of things because I realized I could skip them.

EDIT 2: just to point out. The objective is that the for loop will not go to do one cycle until the previous one is finished. I tried to do this using a while loop to block the cycle, but it didn't work, either.

Answer 1

The https.get function, according to its documentation, does not return a promise.

You can, however, wrap it inside of a function that does return a promise like the following with promiseHttpsGet

const promiseHttpsGet = (url) =>
  new Promise((resolve, reject) => {
    https
      .get(url, (res) => {
        resolve(res);
      })
      .on("error", (er) => {
        reject(er);
      });
  });

async function myFunction(client) {
  const fileC = database();
  const vars = { variable: "my_variable" };
  const url = "my_url";

  let result;

  await fileC.find({}).forEach((f) => fileList.push(f));

  for (const f of fileList) {
    // The helper function returns a promise so you can await that
    const res = await promiseHttpsGet(f.file_location);

    let form = new FormData();

    Object.keys(vars).forEach((key) => form.append(key, vars[key]));
    form.append("file", res, f.file_name);

    // You can await the axios response as well instead of using .then
    const axiosResponse = await axios.post(url, form, {
      headers: form.getHeaders(),
      maxBodyLength: Infinity,
    });

    console.log(response.data.val);
  }
}

Answer 2

OK, I managed to come up with a solution, based on what @crashmstr pointed out about the use of promises. I separated the function for sending the audio from the rest and it worked.

async function getData(f,fileC){
  const vars = {"variable":"my_variable"}
  const url = "my_url"
  return new Promise(function(resolve,reject){
    https.get(f.file_location,function(res){
      let form = new FormData()
      Object.keys(vars).forEach(key=>form.append(key,vars[key]))
      form.append("file",res,f.file_name)
      axios.post(url,form,{headers:form.getHeaders(),maxBodyLength:Infinity}).then((response)=>{
        let value = response == "" //placeholder for actual work
        let update = {"res":response,"value":value}
        resolve(update)
      })
    })
  })
}

async function myFunction(client){
  const fileC = database()
  let result
  await fileC.find({}).forEach(f=>fileList.push(f))
  for (const f of fileList){
    result = await getData(f,fileC)
    await fileC.updateOne(f,{$set:result["update"]})
  }
}

I admit that my experience with promises is quite limited, but this does, at least, serve as a good lesson.