Is there a way to return `assertMsg` error messages defined in the Daml code to the UI?

[gyorgybalazsi]

In the Create Daml App example from the docs, the Daml code defines error messages in the assertMsg satements of the Follow choice:

-- FOLLOW_BEGIN
    nonconsuming choice Follow: ContractId User with
        userToFollow: Party
      controller username
      do
        assertMsg "You cannot follow yourself" (userToFollow /= username)
        assertMsg "You cannot follow the same user twice" (notElem userToFollow following)
        archive self
        create this with following = userToFollow :: following
    -- FOLLOW_END

Though when I try to follow myself I get this error message:

The message comes from this code in the MainView.tsx file:

// FOLLOW_BEGIN
  const ledger = useLedger();

  const follow = async (userToFollow: Party): Promise<boolean> => {
    try {
      await ledger.exerciseByKey(User.User.Follow, username, {userToFollow});
      return true;
    } catch (error) {
      alert(`Unknown error:\n${error}`);
      return false;
    }
  }
  // FOLLOW_END

[Stephen]

What do you get in the alert when you format error to JSON before string-interpolating it?

[gyorgybalazsi]

Thanks, that works, I can extract from this the message already: