How do I get promises to work in the right order in a function?

Question

I'm trying to make a system that generates a radom ID number for a user and then checks if it is already in the mysql database. If it is then it will generate a new ID and check that against the database. It will continue this until it generates a unique identifier and return it to outside the function. I'm pretty new to JavaScript, Node and Asynchronous functions so I don't really know what I'm doing.

I've tried using promises, but the function always just returns "undefined" and checkChatIdExists doesn't finish until afterwards.

generateId() simply returns a 19 digit string and con is a database connection made with MySQL2

function checkChatIdExists(id) {
    return new Promise((resolve, reject) => {
        con.query("SELECT id FROM messages WHERE id = " + id, (err, result)=>{
            if(err !== null) { console.log(err) };
            if(result.length == 0) {
                resolve(id);  //newly generated id is okay
            } else {
                reject("ID was not Unique");         //newly generated id was not okay
            }
        })
    })
}

async function generateChatId() {
    
    async function generateAndCheckIdValid() {
        let id = await generateId();
        console.log("ID generated - " + id);
        checkChatIdExists(id).then((validId) => {
            return validId;       
        }).catch((message) => {
            console.log(message);
            return generateAndCheckIdValid();            //if id does exist then run again
        })
    }

    let id = await generateAndCheckIdValid();
    return id;
}

Answer 1

async function generateAndCheckIdValid() {
  const id = await generateId();
  console.log("ID generated - " + id);
  checkChatIdExists(id)
    .then((validId) => {
      return validId;
    })
    .catch((message) => {
      console.log(message);
      return generateAndCheckIdValid(); //if id does exist then run again
    });
}

This async function has no return statement in it, so it's promise will implicitly resolve to undefined. There's a return statement in a .then callback but that won't do anything of note. I recommend that you don't mix async/await with .then and just stick to one style. Using async/await the code would be:

async function generateAndCheckIdValid() {
  let id = await generateId();
  console.log("ID generated - " + id);
  try {
    const validId = await checkChatIdExists(id);
    return validId;
    // If you prefer, the above 2 lines can be shortened to:
    // return await checkChatIdExists(id);
  } catch (message) {
    console.log(message);
    return generateAndCheckIdValid()
  }
}

If you prefer using .then, you would write the code like this:

function generateAndCheckIdValid() {
  return generateId() // <--- note the `return`
    .then(id => {
       console.log("ID generated - " + id);
       return checkChatIdExists(id);
    })
    // You don't need a .then which just re-returns the value. The promise
    //   is already resolving to that value
    // .then(validId => { return validId })
    .catch(message) => {
      console.log(message);
      return generateAndCheckIdValid();
    });
}