Express JS : Cannot set headers after they are sent to the client

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I have some error when i build auth in express js, there is Cannot set headers after they are sent to the client.

This is my code Before :

 var dataUser = await user.findAll({
    where: {
      email: req.body.email,
      password: req.body.password,
    },
 });
        

if (dataUser) {
   res.send(dataUser);
      // session
      req.session.loggedin = true;
      req.session.role = req.body.role;

}else{
      req.flash('color', 'danger');
      res.redirect('/login');
}

then i just add return on res.send and it’s work now

if (dataUser) {
   return res.send(dataUser);
      // session
      req.session.loggedin = true;
      req.session.role = req.body.role;

}