How to run a function for one item in a for loop before moving on to next item?

Question

    for (var x = 0; x < emails.length; x++){
      var email = emails[x]["email"];
      client.single.check(email, true, true).then(
          result => {
            if (result.getNumericResult() == 0){
              console.log("valid email: "+email);
              var verified = 1;
              admin.database().ref("/users/"+userID+"/emails/"+x+"/verified").set(verified, function(error){
                if (error) {
                  console.log("User ("+userID+") email state could not be saved" + error);
                }
                console.log("Saved");
              });
            }
          },
          err => console.log('ERROR: ' + err.message)
      );
    }

Above is my code.

I have a database entry "emails", which has multiple email addresses, broken out like: (0)-> email: foo@bar.com, (1)-> email: foo1@bar1.com, etc.

What I am trying to do is loop through each email in the emails entry and run a check on that email to validate it. However, I noticed that it will loop to the next item before the validation module (client.single.check) has finished, and as a result will push the wrong "x" (item) in my database path. If it's on the 0th item, it will push to x=1 in the database path where I have "x".

How can I make it so that for each item (email address) in the for loop, it waits to do the email check and also push the result to my database before moving on to the next item in the for loop?

So stuck on this one. Sorry for the newbie question!

The body of your `for` loop makes an asynchronous call, so technically the current iteration finishes before you've received the data you need. Have a look at the Promise API or [async](https://github.com/caolan/async) — djfdev, Nov 08 '17 at 00:06

score 0 · Answer 1 · answered Nov 08 '17 at 00:05

This is because you have async code here. Consider replacing your loop with recursive function something like:

function checkAnotherEmail() {
   // Your code
   result => {
       // Success code
       // Detection if there is a next email
       checkAnotherEmail();
   }
}

How to run a function for one item in a for loop before moving on to next item?

1 Answers1