Function: isInstanceOf()

function isInstanceOf<T>(
  value: unknown,
  type: string,
  ctor?: (...args: any[]) => T,
): value is T;

Returns true if value is an instance of the class identified by type (and optionally ctor).

Type Parameters

Type Parameter	Description
T	The expected instance type.

Parameters

Parameter	Type	Description
value	unknown	The value to test.
type	string	The constructor name to compare against when instanceof is unavailable.
ctor?	(...args: any[]) => T	Optional constructor to use for instanceof and Symbol.hasInstance checks.

Returns

value is T

true when value is an instance of the class described by type/ctor.

Remarks

Performs three checks in order: instanceof ctor, Symbol.hasInstance, then constructor-name comparison. The constructor-name fallback handles cross-realm cases where instanceof fails.