在Array.map函数中使用await

Question

I need to wait for a async function to complete before iterating over the array, the asynchronous function i need to wait to resolve is as follows:

 static async sendEmail (from, to, subject, text) { return new Promise((resolve, reject) => { let message = { from, to, subject, text }; AMMailing.transporter.sendMail(message, function (err, response) { if (err) { reject(err); } else { resolve(response); } }); }); } 

This is the code of the way i'm iterating in the array and trying to wait for it to resolve before it iterates again:

 static sendEmailInQueue (queue) { queue.map(async (person, index) => { console.log('sending email to: ', person.email); try { let success = await AMMailing.sendEmail(AMMailing.message.from, person.email, AMMailing.message.subject, AMMailing.message.text); if (success) { console.log('email sent to: ', person.email); } } catch (err) { console.log(err); } }); } 

My problem is: this line console.log('sending email to: ', person.email); is executed all times and then the AMMailing.sendEmail() function start to log it's results

this is the output i get in the console:

sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
sending email to:  matheus.rezende10@gmail.com
{ Error: Hostname/IP doesn't match certificate's altnames: "Host: mail.appmasters.io. is not in the cert's altnames: DNS:*.sgcpanel.com, DNS:sgcpanel.com"

Answer 1

You don't need to use map in your example, it is not mapping anything. You can simply iterate over your array with for-loop to await on each item sequentially. For example:

static async sendEmailInQueue (queue) { // async method
  for (let i = 0; i < queue.length; i++) {
    try {
      // await sequentially
      let success = await AMMailing.sendEmail(/* ... */);
      if (success) {
        console.log('email sent to: ', person.email);
      }
    } catch (err) {
      console.log(err);
    }
  }
}

Answer 2

You may always use a .reduce() with an initial value of Promise.resove() and sequence your promisified asynchronous tasks.

Assume that our asynchronous sendMail(msg,cb) function sends a mail in 0-250ms. We may promisify it (in case it doesn't return a promise) in our sendMessages function and sequence the promises up with .then() stages within a .reduce() .

 function sendMail(msg, cb){ setTimeout(cb, Math.random()*250, false, "message to: " + msg.to + " is sent"); } function sendMessages(ms){ function promisify(fun, ...args){ return new Promise((v,x) => fun(...args, (err,data) => !!err ? x(err) : v(data))); } ms.reduce((p,m) => p.then(v => promisify(sendMail,m)) .then(v => console.log(v)), Promise.resolve()); } var msgArray = [{from: "x", to: "John@yyz.com", subject: "", text:""}, {from: "y", to: "Rose@ist.com", subject: "", text:""}, {from: "z", to: "Mary@saw.com", subject: "", text:""} ]; sendMessages(msgArray);