Unknown

unknown is the type-safe counterpart of any. Anything is assignable to unknown, but unknown isn’t assignable to anything but itself and any without a type assertion or a control flow based narrowing. Likewise, no operations are permitted on an unknown without first asserting or narrowing to a more specific type.

function f1(a: any) {
  a.b(); // OK
}

function f2(a: unknown) {
  // Error: Property 'b' does not exist on type 'unknown'.
  a.b();
}

Learn more from the following links:

• Unknown Type in TypeScript