Empêcher la soumission du formulaire sur les appels de la fonction onSubmit

returning false here won't be executed and the form will be submitted either way. You should also call preventDefault to prevent the default form action for Ajax form submissions.

function mySubmitFunction(e) {
  e.preventDefault();
  someBug();
  return false;
}

Get more references : https://stackoverflow.com/questions/3350247/how-to-prevent-form-from-being-submitted
Ankur