TypeScript - Best Practices

TypeScript has become the standard in JavaScript application development. With static typing, it helps catch errors at compile time, improves developer experience, and makes code maintenance easier.

1. Use Strict Mode#

Always enable strict mode in tsconfig.json:

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true
  }
}

2. Define Interface Types#

Prefer interface for object definitions:

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

// ❌ Avoid
type User = {
  id: string;
  name: string;
  email: string;
}

3. Use Type Guards#

Type guards allow TypeScript to narrow down types:

function isString(value: unknown): value is string {
  return typeof value === 'string';
}

function processValue(value: string | number) {
  if (isString(value)) {
    // TypeScript knows value is string
    console.log(value.toUpperCase());
  }
}

4. Avoid Any#

The any type disables type checking. Use unknown instead:

// ❌ Avoid
function process(data: any) {
  return data.value;
}

// ✅ Good
function process(data: unknown) {
  if (typeof data === 'object' && data !== null && 'value' in data) {
    return data.value;
  }
}

5. Use Utility Types#

TypeScript offers many useful utility types:

// Partial - all fields optional
type UpdateUser = Partial<User>;

// Pick - select specific fields
type UserPreview = Pick<User, 'id' | 'name'>;

// Omit - omit selected fields
type UserWithoutEmail = Omit<User, 'email'>;

// Readonly - immutable fields
type ImmutableUser = Readonly<User>;

6. Define Return Types#

Always define return types for functions:

// ✅ Good
function getUser(id: string): Promise<User> {
  return fetch(`/api/users/${id}`).then(res => res.json());
}

// ❌ Avoid
function getUser(id: string) {
  return fetch(`/api/users/${id}`).then(res => res.json());
}

7. Organize Types in Modules#

Keep type definitions in dedicated files:

src/
  types/
    user.ts
    product.ts
    api.ts
  components/
  lib/

Summary#

TypeScript is a powerful tool that, when used properly, significantly improves code quality. By following these practices, you create code that is:

• Safer - errors caught at compile time
• More readable - types as documentation
• Easier to maintain - refactoring with confidence

At MDS Software Solutions Group, TypeScript is the standard in all our projects. Contact us to learn more about our services!