node js - how do I return a value from a function when it depends on asynchronous function inside

Question

I've written a node js module that sends emails. The module is a wrapper for the nodemailer module. When the callback of transporter.sendMail is executed, I want my wrapper function to return true if the email was sent, or false otherwise. How can I do this? Here's the code:

var nodemailer = require('nodemailer');

module.exports.sendEmail = function (mailerAddress, mailerPassword, to, subject, html) {
var transporter, mailOptions;

transporter = nodemailer.createTransport({
    service: 'Gmail',
    auth: {
        user: mailerAddress,
        pass: mailerPassword
    }
}); 

mailOptions = {
    from: mailerAddress, 
    to: to,
    subject: subject,
    html: html
};

transporter.sendMail(mailOptions, function(error, info) {
    if (error) {
        return false;
    }
    else {
        return true;
    }
});         
};

there's no error, the problem is I can't return the true or false from the wrapper function. — Mister_L, Nov 09 '15 at 15:38

danilodeveloper · Accepted Answer · 2015-11-09T19:59:47.067

3

If I understood, the "wrapper function" that you're saying is the callback function, so if I I'm correct, try to do something like this:

var EmailUtil = {
    sendEmail : function sendEmail(mailerAddress, mailerPassword, to, subject, html, callback) {
        var options = {
            service: 'Gmail',
            auth: {
                user: mailerAddress,
                pass: mailerPassword
            }
        };
        var transport = nodemailer.createTransport(options);

        transport.sendMail({
            from: mailerAddress, 
            to: to,
            subject: subject,
            html: html
        }, function(err, responseStatus) {
            var val;
            if (error) {
                val = false;
            } else {
                val = true;
            }
            callback(error, val);
        });
    }
};

module.exports = EmailUtil;

This is a real example that I use in production.

edited Nov 09 '15 at 19:59

answered Nov 09 '15 at 16:54

danilodeveloper

3,840
2
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Why do put this way `sendEmail : function sendEmail`? – Jonatas Walker Nov 17 '15 at 15:23
@JonatasWalker this is a very long answer... in short: **1 -** I like to group functions by responsability, for example `EmailUtil` and `EmailOperations`, so inside `EmailUtil` I can create functions like `isEmailValid(...)`, `checkEmailLenght(...)` and inside `EmailOperations` I can create functions like `sendEmail(...)`, `deleteEmail(...)`. **2 -** Write less `module.exports` declarations because the groupings. **3 -** Separation of Concerns. **4 -** And a bit of personal preference :) Of course, we can do this in many ways, your answer is an example of another way to do that. Cheers! – danilodeveloper Nov 17 '15 at 17:02

score 3 · Answer 2 · answered Nov 17 '15 at 15:34

You could also make use of Promises:

Module

module.exports.sendMail = function(mailOptions) {
  var transporter = ....;
  return new Promise(function(resolve, reject) {
    transporter.sendMail(mailOptions, function(error, info) {
      if (error) {
        reject(error);
      } else {
        resolve(info);
      }
    });
  });
};

App

var module = require('...');
var mail = {
  to: '...',
  from: '...'
};
module.sendMail(mail).then(function(response) {
  console.info(response);
}).catch(function(error) {
  console.info(error);
});

score 2 · Answer 3 · edited May 23 '17 at 11:51

2

I'd argue you shouldn't be doing that, because you're effectively trying to turn an async operation into a sync one. If you're intent on this then I'd suggest looking at this answer, which uses async.

Simplest way to wait some asynchronous tasks complete, in Javascript?

edited May 23 '17 at 11:51

Community

1
1

answered Nov 09 '15 at 17:15

Chris Kemp

2,069
2
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Here is an excellent reference to callbacks, promises and Async/ Await: [Async/Await in JavaScript (Youtube) by CodeWorkr, Published on Aug 22, 2017](https://www.youtube.com/watch?v=f57IHEeDNcA) . Repo for video is [here](https://github.com/eXtremeXR/Async-Await) – zipzit Jan 07 '18 at 09:59

node js - how do I return a value from a function when it depends on asynchronous function inside

3 Answers3

Module

App