async await inside async.parallel, callback became undefined

Question

I'm trying to do async/await inside async.parallel, but can't call callback. But if i remove async/await, the callback can be call. Below is the code

let parallelFunc = listCamId.map(camId => {
    return async function (callback) {
      let insertRuleTransParam = {
        rule_id: ruleId,
        camera_id: camId,
        vas_id: vasId,
        additional_parameter: additionalParameter
      }

      let configParamCamera = { where: { id: camId } };
      let configParamRule = { where: { id: ruleId } };

      try {
        let ruleTrans = await createRuleTransaction(insertRuleTransParam);
        let rule = await ruleService.find(configParamRule, "one");
        let cam = await cameraService.find(configParamCamera, "one");
        let uri = await constructCamUri(cam.protocol, cam.user_access, cam.password, cam.ip_address, cam.port, cam.path);
        let visionParam = await startVasRule(vasId, ruleTrans.id, camId, rule.rule_path, rule.rule_exec, uri);
        let updateRuleParam = {
          port_stream: visionParam.port,
          url_stream: visionParam.url,
          mmap_in: visionParam.mmap_in,
          mmap_out: visionParam.mmap_out
        }
        await updateRuleTransaction(updateRuleParam);
        callback(null);
      } catch (e) {
        callback(e);
      }
    }
  })

  return new Promise((resolve, reject) => {
    async.parallel(parallelFunc, function (err, results) {
      if (err) {
        reject(err);
      } else {
        resolve('success');
      }
    })
  });

can someone point out whats wrong with the code?

Never use the async.js library together with promises, even less with async/await syntax. — Bergi
– Bergi, Commented May 4, 2018 at 14:48
do you have suggestion for other way? inside try catch is a sync code, im trying to achieve parallel execution with those sync code for faster time — BIlly
– BIlly, Commented May 4, 2018 at 14:53
@BIllySutomo Bergi is right, async.js became moot with the introduction of promises to the specification. — Patrick Roberts
– Patrick Roberts, Commented May 4, 2018 at 15:01

Bergi · Accepted Answer · 2018-05-04 14:51:27Z

Do not use the async.js library for promise code, and do not use callback parameters. Just use Promise.all to wait for multiple things:

let promises = listCamId.map(async function(camId) {
  let insertRuleTransParam = {
    rule_id: ruleId,
    camera_id: camId,
    vas_id: vasId,
    additional_parameter: additionalParameter
  }

  let configParamCamera = { where: { id: camId } };
  let configParamRule = { where: { id: ruleId } };

  let ruleTrans = await createRuleTransaction(insertRuleTransParam);
  let rule = await ruleService.find(configParamRule, "one");
  let cam = await cameraService.find(configParamCamera, "one");
  let uri = await constructCamUri(cam.protocol, cam.user_access, cam.password, cam.ip_address, cam.port, cam.path);
  let visionParam = await startVasRule(vasId, ruleTrans.id, camId, rule.rule_path, rule.rule_exec, uri);
  let updateRuleParam = {
    port_stream: visionParam.port,
    url_stream: visionParam.url,
    mmap_in: visionParam.mmap_in,
    mmap_out: visionParam.mmap_out
  }
  await updateRuleTransaction(updateRuleParam);
  return null;
});
return Promise.all(promises);

Numman Ali · Accepted Answer · 2019-06-28 10:46:19Z

You CAN use async/await inside async.js

There is a major mistake inside your code:

return async function (callback) {}

Async functions do not need or require a callback, they are shorthand for Promises

Here is a simple example of an async function that will work in async.js:

async function forAsync() {
  try {
    let user = await db.findOne({});
    return user // this is equivalent to resolve(user)
  } catch (e) {
    throw(e) // this is equivalent to reject(err)
  }
}

As a Promise this would be as follows:

function forAsync() {
  return new Promise((resolve,reject) => {
    db.findOne({}, (err,res) => {
      if (err) reject(err)
      let user = res;
      resolve(user);
    });
  }
}

As a callback this would be as follows:

function forAsync(callback) {
  db.findOne({}, (err,res) => {
    if (err) callback(err)     
    let user = res;     
    callback(null, user);
  });
}

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