How can I make this callback code return a boolean?

Question

Node.js

I want to make this function return a boolean value (true - if the entry in the table is found, false otherwise):

function existsEntry(postId){
  db.serialize(function(){
    db.get("SELECT * FROM posts WHERE post_id = ?", [postId], function(err, row){
      if (err) throw err;
            console.log(row);
    });

    db.close();
  });
}

console.log(existsEntry("21706"));

But it's expected to print undefined anyway. How to change her work? I am new to Node

Answer 1

No way.
The only thing that an asynchronous function can return is a Promise, that is, a promise that some value will be received at some point in time.

function existsEntry(postId){
  return new Promise(function (resolve, reject) {
    db.serialize(function(){
      db.get("SELECT * FROM posts WHERE post_id = ?", [postId], function(err, row){
        if (err) {
          resolve(false); // или reject()
        } else {
          resolve(true);
        }
      });

      db.close();
    });
  });
}

existsEntry("21706").then(function (answer) {console.log(answer)});

As soon as you have an asynchronous function, all other code that works with it must also become asynchronous, and you can forget the words "return the result of the function"