Advanced TypeScript Patterns for Large-Scale Applications

As applications grow in complexity, leveraging advanced TypeScript patterns becomes crucial for maintaining code quality, scalability, and developer productivity.

Introduction

TypeScript has evolved far beyond simple type annotations. Modern TypeScript offers powerful features that can help you build more robust and maintainable applications.

Advanced Patterns Covered

1. Conditional Types

type NonNullable<T> = T extends null | undefined ? never : T;

type ApiResponse<T> = {
  data: T;
  error: null;
} | {
  data: null;
  error: string;
};

2. Mapped Types

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

type ReadonlyDeep<T> = {
  readonly [P in keyof T]: T[P] extends object ? ReadonlyDeep<T[P]> : T[P];
};

3. Template Literal Types

type EventName = `on${Capitalize<string>}`;
type Color = "red" | "green" | "blue";
type ButtonColor = `btn-${Color}`;

4. Utility Types for Better APIs

interface User {
  id: string;
  name: string;
  email: string;
  password: string;
}

type PublicUser = Omit<User, "password">;
type UserUpdate = Partial<Pick<User, "name" | "email">>;

Design Patterns

1. Factory Pattern with Generics

abstract class DatabaseAdapter<T> {
  abstract create(data: T): Promise<T>;
  abstract findById(id: string): Promise<T | null>;
  abstract update(id: string, data: Partial<T>): Promise<T>;
  abstract delete(id: string): Promise<void>;
}

2. Builder Pattern

class QueryBuilder<T> {
  private conditions: string[] = [];
  
  where(condition: keyof T, value: any): QueryBuilder<T> {
    this.conditions.push(`${String(condition)} = ?`);
    return this;
  }
  
  build(): string {
    return `SELECT * FROM table WHERE ${this.conditions.join(" AND ")}`;
  }
}

Performance Considerations

• Use const assertions for better type inference
• Leverage satisfies operator for type checking
• Implement proper tree-shaking with module boundaries
• Use declaration files for large external libraries

Testing with Advanced Types

type MockedFunction<T extends (...args: any[]) => any> = T & {
  mockImplementation: (fn: T) => void;
  mockReturnValue: (value: ReturnType<T>) => void;
};

Conclusion

Advanced TypeScript patterns enable you to build more resilient applications with better developer experience. These patterns help catch errors at compile time and provide excellent IntelliSense support.

Start implementing these patterns gradually in your codebase to see immediate improvements in code quality and maintainability.