React 19 types: useRef() with no argument errors 'Expected 1 argument but saw none' — pass an initial value

Fix

- const ref = useRef();
+ const ref = useRef(undefined);
- const Ctx = createContext();
+ const Ctx = createContext(undefined);
- const r: React.MutableRefObject<HTMLDivElement | null> = useRef(null);
+ const r: React.RefObject<HTMLDivElement | null> = useRef(null);

Automated: npx types-react-codemod@latest preset-19 ./src (includes refobject-defaults).

Symptom

After upgrading to @types/react@19, useRef() and createContext() called with no arguments fail type-checking (the upgrade guide annotates them Expected 1 argument but saw none). Code that imports MutableRefObject gets deprecation hints.

Cause

@types/react 19 (React 19 stable 2024-12-05) makes useRef require an argument, like createContext. At the same time all refs became mutable: MutableRefObject is deprecated in favor of a single RefObject<T> { current: T } that useRef always returns. useRef<T>(null) returns RefObject<T | null> and useRef(undefined) returns RefObject<T | undefined>. (The old React 18 annoyance Cannot assign to 'current' because it is a read-only property after useRef<number>(null) is gone.)

Verify

tsc --noEmit passes with @types/react@^19.

Sources

https://react.dev/blog/2024/04/25/react-19-upgrade-guide

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React 19 types: useRef() with no argument errors 'Expected 1 argument but saw none' — pass an initial value

Symptom

Cause

Verify

Sources

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