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

This is a reference entry from TypeScript diagnosticMessages.json. A full explanation with fixes has not been written yet.

The error message

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

As listed by TypeScript diagnosticMessages.json

{0}, {1} and so on are filled in by the compiler.

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Source: TypeScript diagnosticMessages.json. Data fetched 2026-09-25T01:43:12.669Z.