map 中的数组为空，返回 promise - 节点 JS

Question

i am newbie on this. My problem is when I tried to return array full of values, it returned empty. I faced some weeks before and I solved it, declaring the map as a const and returning its value in a function... but I can't remeber how I did it.

This is my code:

module.exports.deleteLockedEmail = (req, res, next) => {
  const maxDateAd = new Date().getTime() - 2592000000;
  const adIdsToDelete = [];
  Admin.find({})
    .then(emailLocked => {
      const mapToLockedEm =  emailLocked.map(element => {
        return User.findOne({email:element.email})
                .then(userLocked => {
                  return adIdsToDelete.push(userLocked)
                })
                .catch(error => console.log(error))
      })
      return mapToLockedEm
    })
    .catch(error => console.log(error))

  cron.schedule("* * * * *", function() {
  console.log("running a task every minute => delete locked ads");
  });
}

How can I fill this array?

adIdsToDelete = [];

Answer 1

Remember that all these calls to database are asynchronous. To get the values you have to wait till the promise is resolved and return values. In this case we can wait for all Promises with Promise.all to be executed and after that in next then context

module.exports.deleteLockedEmail = (req, res, next) => {
  const maxDateAd = new Date().getTime() - 2592000000;
  const adIdsToDelete = [];
  Admin.find({})
    .then(emailLocked => {
      const mapToLockedEm =  emailLocked.map(element => {
        return User.findOne({email:element.email})
                .then(userLocked => {
                  return adIdsToDelete.push(userLocked)
                })
                .catch(error => console.log(error))
      })
      return Promise.all(mapToLockedEm)
    }).then(() => {
      // In this context the adIdsToDelete will be filled
    });
    .catch(error => console.log(error))

  cron.schedule("* * * * *", function() {
  console.log("running a task every minute => delete locked ads");
  });
}

Also in general it can be a little tricky to work with variables like adIdsToDelete as they are in different scope than your promise chain. As it happened in your example - it can be confusing when this variable actually fills with values.

You can rewrite it as following

module.exports.deleteLockedEmail = (req, res, next) => {
  const maxDateAd = new Date().getTime() - 2592000000;
  Admin.find({})
    .then(emailLocked => {
      const mapToLockedEm =  emailLocked.map(element => {
        return User.findOne({email:element.email})
                .catch(error => console.log(error))
      })
      return Promise.all(mapToLockedEm)
    }).then(adIdsToDelete  => {
      // In this context the adIdsToDelete will be filled
    });
    .catch(error => console.log(error))

  cron.schedule("* * * * *", function() {
  console.log("running a task every minute => delete locked ads");
  });
}