Any codebase can quickly devolve into a tangled mess of function calls and copy-pasted snippets, which is difficult to adapt without some upfront discipline and tools that support some consistent organization. If we want our programs to be reusable, concise, and testable without hassle, then we should use dependency injection as a guiding principle to write loosely coupled components. Each piece can focus on doing one thing well while ignoring implementation details that aren’t concerned with it. We can also swap dependencies to control how code behaves in different environments. by Oscar Merida