When working with object types in TypeScript, you often need more flexibility and control than just specifying property names and types. Two powerful features for enhancing object types are optional properties and the readonly modifier. Optional properties allow you to define properties that may or may not be present in an object. To declare an optional property, add a question mark ("?") after the property name. This tells TypeScript that the property is not required when creating objects of that type.

The readonly modifier, on the other hand, ensures that a property cannot be reassigned after the object is created. By adding the readonly keyword before a property name, you prevent accidental changes to that property, helping you enforce immutability where needed. These features are especially useful when designing APIs or working with data structures that should not be altered after initialization.

When defining complex object types, it is important to balance flexibility and safety. Use optional properties for fields that are not always required, but document clearly when those fields are expected. Apply the readonly modifier to properties that should never change after object creation. For nested objects, you can combine these features at any depth, but keep your type definitions clear and maintainable. Consider grouping related properties into nested objects only when it improves clarity or reflects the actual data structure. Avoid making too many properties optional or deeply nesting objects unless necessary, as this can make your types harder to understand and maintain.