TS1228

error TS1228: A type predicate is only allowed in return type position for functions and methods.

Broken Code ❌

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function hasErrorCode(error: any) error is {code: string} {
  return typeof (error && error.code) === 'string'
}

Fixed Code ✔️

You have to separate the argument list from the return type definition by a ::

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function hasErrorCode(error: any): error is {code: string} {
  return typeof (error && error.code) === 'string';
}