Understanding TypeScript Generics

The Problem

Without generics, you'd have to choose between:

1. No type safety — using any
2. No reusability — writing separate functions for each type

typescriptcopy
// Bad: no type safety
function identity(value: any): any {
  return value;
}

// Good: type-safe AND reusable
function identity<T>(value: T): T {
  return value;
}

Generic Constraints

You can constrain generics using extends:

typescriptcopy
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}

Real-World Example

Here's a generic API response wrapper:

typescriptcopy
interface ApiResponse<T> {
  data: T;
  status: number;
  message: string;
}

async function fetchUser(): Promise<ApiResponse<User>> {
  const response = await fetch('/api/user');
  return response.json();
}

Key Takeaways

• Generics let you write flexible, reusable code without sacrificing type safety
• Use extends to constrain what types are allowed
• Constraints like keyof enable powerful utility patterns

Generics take practice — try refactoring some of your existing code to use them.