returning a object gives undefined, using db.all() sqlite3 javascript-CodePudding

I don't understand why its console logging a undefined value instead of the object


function getusername( username ){ 
  let currentUsernameObj;
  sqlDB.all(sql, [username], (err, rows) => {
  if (err) {
    throw err;
  }
  if (!(rows.length === 0)&& username === rows[0].username) {
    console.log(username  " sqn "  rows[0].username );
    console.log(rows[0]);
    currentUsernameObj=rows[0];

  } else {
    console.log("user not found")
  }
  console.log(typeof(currentUsernameObj))
  return currentUsernameObj;
})};
var x=getusername("[email protected]");
console.log(x " yyyyyy");

this is my output output

I was expecting a object to be displayed and don't know what to do

CodePudding user response：

Your callback (see below) will be executed after the function has already returned and since you don't initialize currentUsernameObj to anything it is undefined.

// this callback is called after SQL returns the data
// as DB access is slow this will only be executed after your function has already returned
(err, rows) => {
  if (err) {
    throw err;
  }
  if (!(rows.length === 0)&& username === rows[0].username) {
    console.log(username  " sqn "  rows[0].username );
    console.log(rows[0]);
    currentUsernameObj=rows[0];

  } else {
    console.log("user not found")
  }
  console.log(typeof(currentUsernameObj))
  return currentUsernameObj;
}

You will have to await those results. Unfortunately SQLite does not have a Promise based API to make that easy so you will have to create the Promise yourself.

async function getusername(username) {
  // wrap the function in a Promise
  // resolve the promise on success
  // reject the promise on error
  return new Promise((resolve, reject) => {
    sqlDB.all(sql, [username], (err, rows) => {
      if (err) {
        // promise needs to be rejected as an error occurred
        reject(err)
      }
      if (!(rows.length === 0) && username === rows[0].username) {
        console.log(username   " sqn "   rows[0].username);
        console.log(rows[0]);
        currentUsernameObj = rows[0];
      } else {
        console.log("user not found");
      }
      console.log(typeof currentUsernameObj);
      resolve(currentUsernameObj);
    });
  });
}

// in order to be able to call an async method with await the call has to be in an async method itself
(async () => {
  // we can now use await to wait for the result
  var x = await getusername("[email protected]");
  console.log(x   " yyyyyy");
})();

For more information on async/ await and how to properly handle errors see the JavaScript docs, this tutorial or one of the countless YouTube videos that cover that in detail. Just search for async/ await or Promises.