TS2577

error TS2577: Return type annotation circularly references itself.

Broken Code ❌

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type OurReply = ReturnType<typeof reply>;

function reply(text: string): OurReply {
  if (text === 'Hello') {
    return 'Hi!';
  }

  if (text === 'Goodbye') {
    return 'Bye!';
  }

  return "What's up?";
}

Fixed Code ✔️

You can remove the circular reference by removing the explicit return type (OurReply) from the signature of your function:

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type OurReply = ReturnType<typeof reply>;

function reply(text: string) {
  if (text === "Hello") {
    return "Hi!";
  }

  if (text === "Goodbye") {
    return "Bye!";
  }

  return "What's up?";
}