Type Alias HasOptionalProperty<T, K>

HasOptionalProperty: K extends keyof T
? {} extends Pick<T, K> ? true : false
: false

Test if an object has an optional property.

Type Parameters

T
The object type
K extends PropertyKey
The property key to check

Remarks

Returns true only for properties declared with ?. Does not consider union types that include undefined.

Example

type Obj = { a: string; b?: number; c: number | undefined };
type IsOpt_b = HasOptionalProperty< Obj, 'b' >;  // true
type IsOpt_c = HasOptionalProperty< Obj, 'c' >;  // false