Promises One At A Time?

Question

So it seems I don't quite understand promises, but I've been using them in low code software my company uses for internal tools as a way to perform the same query on different data for a certain number of times.

Anyway, I'm currently using Promises with a Mailgun query, and when I try to resolve Promise.all(promises), I assume I'm hitting them too quickly and too much. So what I would like to do, without having to refactor the entirety of my code, is take what I have and then resolve those Promises one at a time.

let query = Mailgun_MailList_Add_Members;
//let arr = testEmailData.value;
let reps = repInfo.value;
let tableData = table1.selectedRow.data;
let finalResult = [];

for(let i = 0; i < reps.length; i++){
  let emailArr = [];
  let allRepEmails = [];

  /* function that takes an array and checks inside for subarrays, pushing all subvalues into one new array */
  let getAllRepEmails = (arr) => {
    if(arr instanceof Array){
        for(let i = 0; i < arr.length; i++){
            getAllRepEmails(arr[i]);
        }
     }
     else allRepEmails.push(arr); 
  }
  
  for(let j = 0; j < tableData.length; j++){
    /* check if current records owningrep is equal to current index of repinfos lastName */
    if(tableData[j].owningrep.toUpperCase() == reps[i].lastName.toUpperCase()){
      /* takes all the emails from table data in the crrent index and pushes them into array */
      emailArr.push(tableData[j].Emails.replace(/;/g, ",").replace(/:/g, ",").replace(/ +/g, "").replace(/,+/g, ",").split(','));
    }
  }
  /* check inside emailArr for subarrays of emails, pushing emails into new array */
  getAllRepEmails(emailArr);
  /* filters array of all emails for current rep to not include empty strings */
  let noEmptyEmails = _.filter(allRepEmails, el => el != "");
  /* loops over final array of all actual emails, creating objects for each rep with arrays of emails up to 1000 each per API req and pushing them into final array */
  while(noEmptyEmails.length){
      finalResult.push({
        owningrep: reps[i].lastName.toUpperCase(),
        /* converts final email array into JSON format as per API req */
        Emails: JSON.stringify(noEmptyEmails.splice(0,1000))
    });
  }
}
/* maps finalResults to create the promises that perform the query for each record */
let promises = finalResult.map((item) => {
  /* get lastName from repinfo for address variable */
  let name = _.filter(repInfo.value, obj => obj.lastName == item.owningrep)[0].lastName.toLowerCase();
  /* uses name variable and repinfo fromAddress to make address variable representing alias for the mail list we are adding members to */
  let address = _.filter(repInfo.value, obj => obj.lastName == item.owningrep)[0].fromAddress.replace(/^[^@]*/, name + "test");
        query.trigger({
        additionalScope: {
          members: finalResult[finalResult.indexOf(item)].Emails,
          alias: address
        }
      })
  }
);

return Promise.all(promises);

I'm tried using the different methods on Promise to see what happens, I've tried splicing Promises and resolving one. I think the only thing I've learned is that I don't understand Promises.

Does anyone have any ideas?

Answer 1

2 things:

• your finalResult.map((item) => { don't seems to return any promise as TJ explained. I think you meant to do return query.trigger either way that map runs instantly (and in parallel) so the function you have written dosen't really wait for anything so it could be that other chained calls to your function is invoked immediately b/c Promise.all dose not really wait for anything.

The let promises = seems to be an array of undefined values? so again Promise.all(promises) dose nothing for you.

• if you want to run one at the time, then remove finalResult.map((item) => and instead use something like a classic for loop and use async/await:

for (const item of finalResult) {
  await query.trigger(...)
}

your function is required to have the async keyword if you want to use await,
async function foo() { ... }