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Graph/ed37f143-5e7f-45ab-a438-85b075f83629

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exactOptionalPropertyTypes

ed37f143-5e7f-45ab-a438-85b075f83629

exactOptionalPropertyTypes

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Updated7/9/2026

PageRank0.0000

Effectiveness0.000

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PERTAIN_TOSolution

add an `asChild` prop set to `true` — To fix this issue. Tension: This will not render the default DOM element of `SheetTrigger`. Outcome: it will render the child component `` and will pass the props and behaviour of ``.

PERTAIN_TOProblem

error TS2375: Type '{ onFocus: ((record: R) => void) | undefined; }' is not assignable to type 'Props' with 'exactOptionalPropertyTypes: true'. — With `exactOptionalPropertyTypes: true` in tsconfig (TypeScript strict mode). Tension: even though it works at runtime. Outcome: Passing a `T | undefined` value to a child component prop typed as `?: T` is a compile error.

PERTAIN_TORootCause

exactOptionalPropertyTypes: true. Tension: getter and setter types diverge. Outcome: NonNullable<> strips undefined from indexed-access result.

PERTAIN_TOAnswer

Root cause exactOptionalPropertyTypes: true part of TypeScript --strictest / explicit tsconfig opt-in since TS 4.4 redefines what ?: T means. Without it, ?: T is equivalent to T | undefined — the key can hold undefined explicitly. With it, ?: T means the key must be absent not present at all when there is no value; undefined is not a valid value for the key. When a parent destructures its own optional prop { onFocus }: { onFocus?: Fn }, TypeScript widens the local variable type to Fn | undefined because the binding is always defined, just possibly undefined. Passing that Fn | undefined to a child prop typed onFocus?: Fn then fails: the child expects the key to be absent, not set to undefined. Solution: conditional spread at the JSX call site tsx // WRONG — TS2375 with exactOptionalPropertyTypes: <Child onFocus={parentOnFocus} / // CORRECT — conditional spread: <Child {...parentOnFocus !== undefined ? { onFocus: parentOnFocus } : {}} / The spread either adds the key with a concrete Fn value, or adds nothing. TypeScript sees that when parentOnFocus is undefined the key is structurally absent from the spread object, satisfying the exactOptionalPropertyTypes constraint. Runtime behavior is identical. Why the other approaches fail | Approach | Why it fails | |----------|-------------| | onFocus={onFocus ?? undefined} | undefined ?? undefined is still undefined; the key is still present | | onFocus={onFocus!} | Non-null assertion lies to the type system; crashes at runtime if onFocus is actually undefined | | Casting as Fn | Same lie; unsafe | | Disabling exactOptionalPropertyTypes | Loses the whole-tsconfig safety guarantee | Alternative: helper utility type If this pattern appears frequently, a utility type can make intent explicit: ts type OptionalProps<T = { K in keyof T as undefined extends TK ? K : never?: Exclude<TK, undefined } But the conditional spread is simpler and more readable at the call site. Verification pnpm typecheck or tsc --noEmit goes from TS2375 errors to 0 after switching to the conditional spread pattern. Applies to all optional callback props passed from an outer optional binding in React JSX under exactOptionalPropertyTypes: true. Environment - TypeScript 4.4+ when exactOptionalPropertyTypes was introduced - React any version using JSX - tsconfig: "exactOptionalPropertyTypes": true either explicit or via "strict": true in future TS versions that may enable it by default

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