Type Alias OptionalKeys<R>

OptionalKeys: PickUndefined<MapToNever<R>>

Extracts keys from a record R that are explicitly marked as optional using the ? modifier. It works by creating a mapped type where all values are never and then using PickUndefined to find keys where undefined is assignable (which is true only for optional properties in this context).

Type Parameters

R extends UnknownRecord
The record type.

Returns

A union of keys that are optional in R.

Example

type K = OptionalKeys<{
  a?: 0; // optional
  b?: 0 | undefined; // optional
  c?: undefined; // optional
  d: 0; // required
  e: undefined; // required, value is undefined
  f: 0 | undefined; // required, value includes undefined
}>; // 'a' | 'b' | 'c'

Type Alias OptionalKeys<R>

Type Parameters

Returns

Example

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