TypeScript Best Practices for 2025

TypeScript has become the standard for building large-scale JavaScript applications. Here are the best practices I follow in every project.

1. Use Strict Mode — Always

Enable strict: true in your tsconfig.json. This single flag enables a suite of strict type-checking options:

{
  "compilerOptions": {
    "strict": true
  }
}

This catches bugs early — null reference errors, implicit any types, and more.

2. Prefer interface for Object Shapes

While type and interface are largely interchangeable, I prefer interface for defining object shapes:

// ✅ Preferred
interface User {
  id: string;
  name: string;
  email: string;
}

// Also fine for unions, intersections, etc.
type Status = 'active' | 'inactive' | 'suspended';

Interfaces are extendable and produce better error messages.

3. Avoid any — Use unknown Instead

// ❌ Don't do this
function process(data: any) {
  data.foo.bar; // No type safety!
}

// ✅ Do this
function process(data: unknown) {
  if (typeof data === 'object' && data !== null && 'foo' in data) {
    // Now TypeScript knows the shape
  }
}

4. Leverage Utility Types

TypeScript ships with powerful built-in utility types:

interface Todo {
  title: string;
  description: string;
  completed: boolean;
}

// Make all properties optional
type PartialTodo = Partial<Todo>;

// Make all properties required
type RequiredTodo = Required<Todo>;

// Pick specific properties
type TodoPreview = Pick<Todo, 'title' | 'completed'>;

// Omit specific properties
type TodoInfo = Omit<Todo, 'completed'>;

5. Use const Assertions

// Without const assertion — type is string[]
const colors = ['red', 'green', 'blue'];

// With const assertion — type is readonly ["red", "green", "blue"]
const colors = ['red', 'green', 'blue'] as const;

This gives you literal types and readonly tuples — perfect for configuration objects and constants.

6. Discriminated Unions for State Management

type LoadingState = { status: 'loading' };
type SuccessState = { status: 'success'; data: string[] };
type ErrorState = { status: 'error'; error: Error };

type State = LoadingState | SuccessState | ErrorState;

function handleState(state: State) {
  switch (state.status) {
    case 'loading':
      return 'Loading...';
    case 'success':
      return state.data.join(', '); // TS knows data exists
    case 'error':
      return state.error.message; // TS knows error exists
  }
}

Discriminated unions are one of TypeScript’s most powerful patterns. Use them to model complex state machines safely.

Conclusion

TypeScript is more than just “JavaScript with types” — it’s a tool that fundamentally changes how you think about code reliability. Adopt these practices and you’ll write code that’s not just type-safe, but genuinely better.