How to generate unique username by checking again and again in database?

Question

I am writing a function to generate a unique username for each new user. At first, assign a username matching with the full name of the user, then check that it exists in your database or not. If it exists then add some number to it and then check again until you come up with a new username that does not exist in the database.

Below is the code for the same

var generateUsername = function(name){
                var username = name;
                console.log(username);
                var isUsername;
                var number = 0;
                db.collection("users").where("username", "==", username)
                .get()
                .then(function(querySnapshot) {
                    if(querySnapshot.empty){
                        isUsername = false;
                    }
                    else {
                        isUsername = true;
                    }

                    while(isUsername == true){
                        number++;
                        username = fullName + number;
                        console.log(username);
                        db.collection("users").where("username", "==", username)
                        .get()
                        .then(function(querySnapshot) {
                            if(querySnapshot.empty){
                                isUsername = false;
                            }
                            else {
                                isUsername = true;
                            }
                        })
                        .catch(function(error) {
                            console.log("Error getting documents: ", error);
                        });
                    }
                })
                .catch(function(error) {
                    console.log("Error getting documents: ", error);
                });
            }

This is not giving me desired output. The loop is running infinitely. Whhere I am doing wrong?

Answer 1

So after andy mccullough suggestion, I came up with below solution

var generateUsername = function(name){
                var username = name;
                var isUsername;
                var number = 0;
                db.collection("users").where("username", "==", username).get()
                .then(function(querySnapshot) {
                    if(querySnapshot.empty){
                        isUsername = false;
                    }
                    else {
                        isUsername = true;
                    }
                    (async function loop(){
                        while(isUsername == true){
                            number++;
                            username = name + number;
                            var querySnapshot = await db.collection("users").where("username", "==", username).get();
                            if(querySnapshot.empty){
                                isUsername = false;
                            }
                            else {
                                isUsername = true;
                            }
                        }
                        console.log(username);
                    })();

                })
                .catch(function(error) {
                    console.log("Error getting documents: ", error);
                });
            }

It is necessary to wait loop function till database returns a promise. Using async await this can be acheived. You can refer to this answer for more details JavaScript ES6 promise for loop