Uncaught TypeError: Cannot read property 'get' of undefined error

Question

I am trying to use either the email or username of the User class to login. However, when I query for the email and try to do

object.get("username") 

I get the error message above. Strangely, when I test the helper function getUsername in the debugger it works fine

function getUsername(email) {
  var query = new Parse.Query(Parse.User);
  query.equalTo('email', email);
  query.first({
    success: function(object) {
      console.log(object.get("username"));
      return object.get("username");
    },
    error: function(user, error) {
      console.log("no email");
    }
  });
}


function signIn(usernameOrEmail, password) {

  //if not email sign in with username
  if (usernameOrEmail.indexOf("@") == -1) {
    Parse.User.logIn(usernameOrEmail, password, {
      success: function(user) {
        console.log("Logged in!");
      },
      error: function(user, error) {
        alert("Error: " + error.code + " " + error.message);
      }
    });
  }
  //query for username from email and signin
  else {
    var username = getUsername(usernameOrEmail);
    Parse.User.logIn(username, password, {
      success: function(user) {
        console.log("Logged in!");
      },
      error: function(user, error) {
        alert("Error: " + error.code + " " + error.message);
      }
    });
  }
}

Solution

query.first is an asynchronous function. To use the values it returns, you have to do it in the success: callback function. So pass a callbak to getUsername that performs the login.

function getUsername(email, callback) {
  var query = new Parse.Query(Parse.User);
  query.equalTo('email', email);
  query.first({
    success: function(object) {
      if (object) {
        console.log(object.get("username"));
        callback(object.get("username"));
      } else {
        console.log("email not found");
      }
    },
    error: function(user, error) {
      console.log("no email");
    }
  });
}

function signIn(usernameOrEmail, password) {

  //if not email sign in with username
  if (usernameOrEmail.indexOf("@") == -1) {
    Parse.User.logIn(usernameOrEmail, password, {
      success: function(user) {
        console.log("Logged in!");
      },
      error: function(user, error) {
        alert("Error: " + error.code + " " + error.message);
      }
    });
  }
  //query for username from email and signin
  else {
    getUsername(usernameOrEmail, function(username) {
        signIn(username, password);
    });
  }
}