For my registration page, I want to check for existing users before adding a new user to avoid duplicate usernames. For some reason, after I check if an existing username exists in the database, it does not run any of the code afterwards.

app.post("/register", (req, res) => {
  const username = req.body.username;
  const password = req.body.password;
  var newuser = false;

  db.query("SELECT * FROM users WHERE username = ?;", [username], (err, result) => {
      
    if (err) {
      res.send({err: err})
    }

    if (result.length == 0) {
      newuser = true;
      console.log(newuser   "one")
    }
  })

    if (newuser) {
    console.log(newuser   "two")
    bcrypt.hash(password, saltRounds, (err, hash) => {
      if (err)
      console.log(err)
    
      db.query(
        "INSERT INTO users (username, password) VALUES (?,?)",
        [username, hash],
        (err, result) => {
        if (err)
          console.log(err);
          }
      )
    })
  }
})

<iframe name="sif1" sandbox="allow-forms allow-modals allow-scripts" frameborder="0"></iframe>

In this example, the only output I get is "trueone" ... meaning that it evaluated result.length to 0 and set newuser = true.

CodePudding user response：

It is because you are not waiting to the result of the first select. You can use async function or move the if(new user) condition into the select callback.