Dependency injection (DI) is a design pattern that allows for the swapping of components required for code execution, making it adaptable to changes in the environment and enhancing reusability in Object-Oriented Programming. In React, DI is particularly useful for mocking and testing components, although it is not mandatory as it is in Angular. By injecting dependencies, React components can be tested and documented without affecting production data or performance, as shown with the use of custom hooks and the Context API. This approach, illustrated with tools like Storybook and React Query, allows developers to override or redefine dependencies to suit different environments efficiently. While DI offers benefits like easy implementation and native support in JavaScript, it can also clutter imports and component props, potentially causing confusion. The discussion highlights when DI is advantageous and when other methods, like interceptors, might be more appropriate for certain tasks.