Unable to wait for async call in Javascript

Question

I have a call to AWS where I get a response and the callback looks like so:

const handleResponse = async (response) => {
  var responseBody = "";
  response.on("data", async function (chunk) {
    responseBody += chunk;
  });
  response.on("end", async function (chunk) {
    return responseBody;
  });
  return responseBody;
};

My current attempt is to call this function with an await like such:

const getLoadIds = async (payload) => {
  //   console.log(payload);
  const resp = await handleResponse(payload)
  console.log(resp) <--- this is undefined
}

How can I get the response from the response.on("end") call?

Here is the original caller code:

  var client = new AWS.HttpClient();
  try {
    await client.handleRequest(request, null, async (res) => fn(res));
  } catch (err) {

fn is an alias to getLoadIds

handleResponse is not doing anything asynchronously... It just immediately returns the empty string. — Niet the Dark Absol
– Niet the Dark Absol, Commented Sep 22, 2021 at 16:48
That is because you are returning right away from handleResponse. To do this, remove async from the function, then return a promise instead from handleResponse that resolves to responseBody when the end event occurs. Remove async from your callbacks. — Andrew Li
– Andrew Li, Commented Sep 22, 2021 at 16:48

Andrew Li · Accepted Answer · 2021-09-22 16:56:40Z

1

You might want to have something like

const handleResponse = (response) => {
  return new Promise((resolve) => {
    var responseBody = "";
    response.on("data", function (chunk) {
      responseBody += chunk;
    });
    response.on("end", function (chunk) {
      resolve(responseBody);
    });
  });
};

upd: thanx @Andrew Li, noticed bug issue in the answer

edited Sep 22, 2021 at 16:56

Andrew Li

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answered Sep 22, 2021 at 16:52

Alex Shtromberg

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1 Comment

Bergi Over a year ago

Don't forget error handling though

Andy · Accepted Answer · 2021-09-22 17:02:55Z

0

Wrap the stream handler in a promise. resolve it if returns data, and reject if it has an error.

function handleResponse() {
  let responseBody = '';
  return new Promise((res, rej) => {
    response.on('data', (chunk) => responseBody += chunk);
    response.on('end', () => res(responseBody));
    response.on('error', (error) => rej(error));
  });
};

function getLoadIds(payload) {
  const resp = await handleResponse(payload);
  console.log(resp);
}

answered Sep 22, 2021 at 17:02

Andy

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