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Module 35: TypeScript Future & Best Practices

Explore upcoming TypeScript features, community best practices, and patterns for writing maintainable, scalable TypeScript code.

1. TypeScript Roadmap​

Upcoming Features​

TypeScript Evolution

TypeScript continuously evolves with ECMAScript proposals and community feedback.

// Stage 3 Decorators (coming in TypeScript 5.0+)
function log(target: any, context: ClassMethodDecoratorContext) {
    return function(...args: any[]) {
        console.log(`Calling ${String(context.name)}`);
        return target.apply(this, args);
    };
}

class Service {
    @log
    process() {
        console.log("Processing...");
    }
}

// Using keyword (proposal)
import { helper using resource } from "./utils";
// Resource automatically cleaned up

2. Best Practices​

2.1 Avoid any​

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

// ✅ Good
function process<T extends { value: unknown }>(data: T) {
    return data.value;
}

// ✅ Better - use unknown when type is truly unknown
function processUnknown(data: unknown) {
    if (typeof data === "object" && data !== null && "value" in data) {
        return (data as { value: unknown }).value;
    }
}

2.2 Use Strict Mode​

{
    "compilerOptions": {
        "strict": true,
        "noImplicitAny": true,
        "strictNullChecks": true,
        "strictFunctionTypes": true,
        "strictBindCallApply": true,
        "strictPropertyInitialization": true,
        "noImplicitThis": true,
        "alwaysStrict": true
    }
}

2.3 Prefer interface for Objects​

// ✅ Good - interface for object shapes
interface User {
    id: string;
    name: string;
}

// ✅ Good - type for unions, primitives, computed types
type ID = string | number;
type Status = "active" | "inactive";
type UserWithStatus = User & { status: Status };

2.4 Use Readonly​

// ✅ Good - prevent mutations
interface Config {
    readonly apiUrl: string;
    readonly timeout: number;
}

// ✅ Use ReadonlyArray for arrays
function sum(numbers: ReadonlyArray<number>): number {
    return numbers.reduce((a, b) => a + b, 0);
}

// ✅ Use as const for literal types
const config = {
    env: "production",
    port: 3000
} as const;

2.5 Type Guards Over Type Assertions​

// ❌ Bad - type assertion
function getLength(value: string | string[]) {
    return (value as string[]).length;  // Unsafe
}

// ✅ Good - type guard
function getLength(value: string | string[]): number {
    if (Array.isArray(value)) {
        return value.length;  // Safe
    }
    return value.length;
}

// ✅ Custom type guard
function isUser(value: unknown): value is User {
    return (
        typeof value === "object" &&
        value !== null &&
        "id" in value &&
        "name" in value
    );
}

2.6 Discriminated Unions​

// ✅ Excellent pattern
type Result<T, E = Error> =
    | { success: true; value: T }
    | { success: false; error: E };

function parseJSON<T>(json: string): Result<T> {
    try {
        return { success: true, value: JSON.parse(json) };
    } catch (error) {
        return { success: false, error: error as Error };
    }
}

// Type-safe handling
const result = parseJSON<User>(jsonString);
if (result.success) {
    console.log(result.value.name);  // Type: User
} else {
    console.error(result.error.message);  // Type: Error
}

2.7 Utility Types​

// ✅ Use built-in utility types
type PartialUser = Partial<User>;
type RequiredUser = Required<User>;
type ReadonlyUser = Readonly<User>;
type PickedUser = Pick<User, "id" | "name">;
type OmittedUser = Omit<User, "password">;

// ✅ Combine utilities
type CreateUserDTO = Omit<User, "id" | "createdAt">;
type UpdateUserDTO = Partial<CreateUserDTO>;

2.8 Async Best Practices​

// ✅ Good - proper error handling
async function fetchUser(id: string): Promise<User> {
    try {
        const response = await fetch(`/api/users/${id}`);
        if (!response.ok) {
            throw new Error(`HTTP error! status: ${response.status}`);
        }
        return await response.json();
    } catch (error) {
        if (error instanceof Error) {
            throw new Error(`Failed to fetch user: ${error.message}`);
        }
        throw error;
    }
}

// ✅ Use Promise.all for parallel operations
async function fetchUserData(id: string) {
    const [user, posts, comments] = await Promise.all([
        fetchUser(id),
        fetchPosts(id),
        fetchComments(id)
    ]);
    return { user, posts, comments };
}

2.9 Naming Conventions​

// ✅ Good naming
interface User {}                    // PascalCase for types/interfaces
type UserId = string;               // PascalCase for type aliases
const MAX_RETRY_COUNT = 3;          // UPPER_CASE for constants
function getUserById(id: string) {} // camelCase for functions
class UserService {}                // PascalCase for classes

// Generic type parameters
// T = Type, K = Key, V = Value, E = Element
function map<T, U>(items: T[], fn: (item: T) => U): U[] {
    return items.map(fn);
}

2.10 Documentation​

/**
 * Fetches user data from the API
 * @param id - The unique user identifier
 * @returns Promise resolving to User object
 * @throws {NotFoundError} When user doesn't exist
 * @throws {NetworkError} When network request fails
 * @example
 * ```typescript
 * const user = await fetchUser("123");
 * console.log(user.name);
 * ```
 */
async function fetchUser(id: string): Promise<User> {
    // Implementation
}

3. Performance Optimization​

3.1 Type-Only Imports​

// ✅ Good - faster compilation
import type { User } from "./types";
import { api } from "./api";

// ✅ Export types separately
export type { User, Post };
export { createUser, getUser };

3.2 Skip Lib Check​

{
    "compilerOptions": {
        "skipLibCheck": true  // Faster compilation
    }
}

3.3 Incremental Compilation​

{
    "compilerOptions": {
        "incremental": true,
        "tsBuildInfoFile": ".tsbuildinfo"
    }
}

4. Testing Best Practices​

// ✅ Type-safe tests
import { describe, it, expect } from "vitest";

describe("UserService", () => {
    it("should create user", async () => {
        const service = new UserService();
        const user = await service.createUser({
            name: "John",
            email: "john@example.com"
        });

        expect(user).toHaveProperty("id");
        expect(user.name).toBe("John");
    });
});

// ✅ Type-safe mocks
const mockRepository: jest.Mocked<UserRepository> = {
    findById: jest.fn(),
    save: jest.fn(),
    delete: jest.fn()
};

5. Security Best Practices​

// ✅ Validate input
import { z } from "zod";

const userSchema = z.object({
    name: z.string().min(1).max(100),
    email: z.string().email(),
    age: z.number().min(0).max(150)
});

type User = z.infer<typeof userSchema>;

function createUser(input: unknown): User {
    return userSchema.parse(input);  // Throws on invalid input
}

// ✅ Sanitize output
function sanitizeUser(user: User): PublicUser {
    return {
        id: user.id,
        name: user.name
        // password excluded
    };
}

6. Code Organization​

src/
├── types/
│   ├── index.ts         // Export all types
│   ├── user.ts
│   └── post.ts
├── services/
│   ├── user.service.ts
│   └── post.service.ts
├── repositories/
│   ├── user.repository.ts
│   └── post.repository.ts
├── controllers/
│   ├── user.controller.ts
│   └── post.controller.ts
├── utils/
│   ├── validation.ts
│   └── errors.ts
└── index.ts

7. Community Resources​

Learning Resources​

Tools​

  • ts-node - Execute TypeScript directly
  • tsx - Fast TypeScript execution
  • tsc-watch - Watch mode utilities

Libraries​

8. Migration Checklist​

☑ Install TypeScript and @types packages
☑ Create tsconfig.json
☑ Enable strict mode gradually
☑ Convert files incrementally
☑ Add type annotations
☑ Replace any with proper types
☑ Add JSDoc comments
☑ Set up linting (ESLint + TypeScript)
☑ Configure build process
☑ Update CI/CD pipeline
☑ Train team on TypeScript
☑ Document patterns and conventions

9. Final Best Practices Summary​

PracticeRecommendation
Type SafetyUse strict mode, avoid any
NullabilityUse strictNullChecks, handle null/undefined
ImmutabilityPrefer readonly, ReadonlyArray, as const
Type GuardsUse type guards over assertions
GenericsUse constraints, avoid over-engineering
Error HandlingUse custom error classes, Result types
TestingWrite type-safe tests with proper mocks
DocumentationUse TSDoc for public APIs
PerformanceUse type-only imports, incremental builds
OrganizationSeparate types, consistent structure

Key Takeaways​

✅ Strict mode catches more bugs
✅ Avoid any - use unknown instead
✅ Type guards over assertions
✅ Discriminated unions for safer code
✅ Utility types for transformations
✅ Documentation improves maintainability
✅ Performance matters in large projects
✅ Stay updated with TypeScript releases

Congratulations! 🎉​

You've completed all 35 modules of the TypeScript tutorial! You now have:

  • ✅ Solid understanding of TypeScript fundamentals
  • ✅ Advanced type system knowledge
  • ✅ Real-world project experience
  • ✅ Best practices and patterns
  • ✅ Interview preparation
  • ✅ Tools and ecosystem familiarity

Continue Learning​

  • Build real projects with TypeScript
  • Contribute to open-source TypeScript projects
  • Stay updated with TypeScript releases
  • Practice type challenges regularly
  • Share knowledge with the community

Practice Exercises​

Exercise 1: Build Production App​

Create a full-stack application with TypeScript, implementing all best practices learned.

Exercise 2: Contribute to Open Source​

Find a TypeScript open-source project and contribute.

Exercise 3: Create Type Library​

Build a utility type library with comprehensive tests and documentation.

Thank you for completing this comprehensive TypeScript tutorial! Keep coding and exploring! 🚀