immutability-helper

const isEquals: any;

_default: <T, C extends CustomCommands<object> = never>(
    object: T,
    $spec: Spec<T, C>
) => T;

extend: <T>(directive: string, fn: (param: any, old: T) => T) => void;

invariant: (condition: boolean, message: () => string) => void;

type CustomCommands<T> = T & {
    __noInferenceCustomCommandsBrand: any;
};

type Spec<T, C extends CustomCommands<object> = never> =
    | (T extends Array<infer U> | ReadonlyArray<infer U>
          ? ArraySpec<U, C>
          : T extends Map<infer K, infer V> | ReadonlyMap<infer K, infer V>
          ? MapSpec<K, V, C>
          : T extends Set<infer X> | ReadonlySet<infer X>
          ? SetSpec<X>
          : T extends object
          ? ObjectSpec<T, C>
          : never)
    | {
          $set: T;
      }
    | {
          $apply: (v: T) => T;
      }
    | ((v: T) => T)
    | (C extends CustomCommands<infer O> ? O : never);