TypeScript Best Practices for 2025

TypeScript has become the standard for building robust JavaScript applications. As we move into 2025, let's revisit the best practices that will keep your TypeScript code clean and maintainable.

Strict Mode Is Your Friend

Always enable strict mode in your `tsconfig.json`. It catches more bugs at compile time and forces you to write better code.

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true
  }
}

These settings might seem restrictive at first, but they prevent countless runtime errors.

Type Inference vs Explicit Types

TypeScript's type inference is powerful. Let the compiler do the work when possible:

// ❌ Unnecessary explicit type
const count: number = 5;

// ✅ Let TypeScript infer const count = 5;

// ✅ Explicit types where they add value function processUser(id: string): Promise<User> { return fetchUser(id); } ```

Use explicit types for function parameters and return values, but let inference handle local variables.

Avoid the `any` Type

The `any` type defeats the purpose of TypeScript. Use `unknown` instead when you truly don't know the type:

// ❌ Loses all type safety
function processData(data: any) {
  return data.value;
}

// ✅ Forces type checking function processData(data: unknown) { if (typeof data === 'object' && data !== null && 'value' in data) { return (data as { value: unknown }).value; } throw new Error('Invalid data'); } ```

Discriminated Unions

Use discriminated unions for type-safe state management:

type LoadingState = 
  | { status: 'idle' }
  | { status: 'loading' }
  | { status: 'success'; data: User }
  | { status: 'error'; error: Error };

function handleState(state: LoadingState) { switch (state.status) { case 'success': // TypeScript knows state.data exists here return state.data.name; case 'error': // TypeScript knows state.error exists here return state.error.message; default: return 'Loading...'; } } ```

This pattern eliminates entire classes of runtime errors.

Utility Types Are Powerful

TypeScript's built-in utility types save time and make code more maintainable:

interface User {
  id: string;
  name: string;
  email: string;
  role: 'admin' | 'user';
}

// Pick only needed fields type UserPreview = Pick<User, 'id' | 'name'>;

// Make all fields optional type PartialUser = Partial<User>;

// Make all fields readonly type ImmutableUser = Readonly<User>;

// Omit sensitive fields type PublicUser = Omit<User, 'email'>; ```

Generic Constraints

Use generic constraints to make your functions more flexible yet type-safe:

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

const user = { name: 'Andre', age: 25 }; const name = getProperty(user, 'name'); // Type: string const age = getProperty(user, 'age'); // Type: number ```

Const Assertions

Use `as const` for truly immutable values and better type inference:

// Without const assertion
const routes = {
  home: '/',
  about: '/about',
}; // Type: { home: string; about: string; }

// With const assertion const routes = { home: '/', about: '/about', } as const; // Type: { readonly home: "/"; readonly about: "/about"; } ```

Type Guards

Create custom type guards for runtime type checking:

function isUser(value: unknown): value is User {
  return (
    typeof value === 'object' &&
    value !== null &&
    'id' in value &&
    'name' in value
  );
}

function processValue(value: unknown) { if (isUser(value)) { // TypeScript knows value is User here console.log(value.name); } } ```

Conclusion

TypeScript is a powerful tool, but only if used correctly. Enable strict mode, avoid `any`, use discriminated unions, leverage utility types, and create type guards. These practices will make your code more maintainable and catch bugs before they reach production.

The investment in proper TypeScript usage pays dividends in reduced debugging time and increased confidence in your codebase.