Function extend

extend<Defaults extends object = object, Options extends object = object>(
defaultOptions?: Defaults,
options?: Options,
): Merge<Defaults, Options>
Deeply copies Adapter options and fills missing properties from defaults.

This intentionally preserves the v1 recursive merge order: at nested levels, the existing option object becomes the recursive defaults argument. Code which needs conventional deep-merge semantics should use a dedicated merge utility instead.
Type Parameters
- Defaults extends object = object
- Options extends object = object
Parameters
- OptionaldefaultOptions: Defaults
  Values used when the corresponding option is absent.
- Optionaloptions: Options
  User-supplied values copied into the result.
Returns Merge<Defaults, Options>
- Defined in util.ts:70