Dependency Injection Patterns in TypeScript

Dependency Injection (DI) is a design pattern where objects receive their dependencies from external sources rather than creating them internally. This creates loosely-coupled, testable, and maintainable code.

The Problem#

Constructor Injection#

Interface-Based Injection#

Factory Pattern#

IoC Container (InversifyJS)#

TSyringe (Simpler Alternative)#

Functional Approach#

React Context for DI#

Testing with DI#

Best Practices#

1. Inject Interfaces, Not Implementations#

2. Prefer Constructor Injection#

3. Keep Dependencies Minimal#

Conclusion#

Dependency injection creates flexible, testable code. Start with simple constructor injection—you don't always need a full IoC container. The key is depending on abstractions and receiving dependencies from outside.

Choose the approach that fits your project: manual injection for simple apps, factories for medium complexity, and IoC containers for large applications with many dependencies.