Advanced TypeScript Patterns for Large-Scale Applications

TypeScript in Modern Development

TypeScript has become an essential tool for building large-scale JavaScript applications. Its static typing system helps catch errors early and improves code maintainability.

Advanced Types

TypeScript offers powerful type constructs that go beyond basic types.

Conditional Types

Conditional types allow you to create types that depend on other types.

type IsString = T extends string ? true : false;

type A = IsString;  // true
type B = IsString;  // false

Mapped Types

Mapped types allow you to create new types by transforming properties of existing types.

type Readonly = {
    readonly [P in keyof T]: T[P];
};

type Partial = {
    [P in keyof T]?: T[P];
};

interface User {
    name: string;
    age: number;
}

type ReadonlyUser = Readonly;
type PartialUser = Partial;

Utility Types

TypeScript provides several built-in utility types for common type transformations.

Common Utility Types

• Partial - Makes all properties optional
• Required - Makes all properties required
• Readonly - Makes all properties readonly
• Pick - Picks specific properties
• Omit - Omits specific properties

// Example usage
interface User {
    id: number;
    name: string;
    email: string;
    createdAt: Date;
}

// Create a type for user creation (without id and timestamps)
type CreateUserInput = Omit;

// Create a type for user updates (all optional except id)
type UpdateUserInput = Partial> & { id: number };

Advanced Patterns

Branded Types

Branded types help prevent mixing incompatible values of the same primitive type.

type UserId = string & { readonly __brand: 'UserId' };
type PostId = string & { readonly __brand: 'PostId' };

function createUserId(id: string): UserId {
    return id as UserId;
}

function createPostId(id: string): PostId {
    return id as PostId;
}

// This will cause a type error
const userId: UserId = createUserId('123');
const postId: PostId = userId; // Error!

These advanced TypeScript patterns enable building more robust and maintainable large-scale applications.