# API Integration Standards for TypeScript
This document outlines the standards and best practices for integrating with backend services and external APIs in TypeScript projects. Adhering to these guidelines will result in more maintainable, performant, and secure code.
## 1. Architectural Considerations
### 1.1. Abstraction and Decoupling
**Standard:** Decouple API interaction logic from core application logic using abstraction layers.
**Why:** This separates concerns, improves testability, reduces dependencies, and allows for easier switching of API implementations without affecting the rest of the application.
**Do This:**
"""typescript
// api-client.ts
export interface APIClient {
fetchData(endpoint: string): Promise;
}
export class DefaultAPIClient implements APIClient {
async fetchData(endpoint: string): Promise {
const response = await fetch(endpoint);
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
}
}
// service.ts
import { APIClient, DefaultAPIClient } from './api-client';
export class MyService {
private apiClient: APIClient;
constructor(apiClient: APIClient = new DefaultAPIClient()) {
this.apiClient = apiClient;
}
async getData(): Promise {
return this.apiClient.fetchData('/api/data');
}
}
"""
**Don't Do This:**
"""typescript
// service.ts (Anti-pattern: Tightly coupled API call)
export class MyService {
async getData(): Promise {
const response = await fetch('/api/data');
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
}
}
"""
### 1.2. Centralized API Configuration
**Standard:** Store API endpoints, timeouts, and authentication details in a centralized configuration.
**Why:** Easier management of API configurations across the application, enabling quick updates and environment-specific configurations. Leveraging environment variables is crucial.
**Do This:**
"""typescript
// config.ts
export const API_CONFIG = {
baseURL: process.env.REACT_APP_API_BASE_URL || 'https://api.example.com',
timeout: 5000, // milliseconds
apiKey: process.env.REACT_APP_API_KEY,
};
// api-client.ts
import { API_CONFIG } from './config';
export class DefaultAPIClient {
async fetchData(endpoint: string): Promise {
try {
const response = await fetch("${API_CONFIG.baseURL}${endpoint}", {
headers: {
'x-api-key': API_CONFIG.apiKey || ''
},
signal: AbortSignal.timeout(API_CONFIG.timeout)
});
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
} catch (error) {
console.error("API Fetch Error:", error);
throw error; // Re-throw to allow calling code to handle the error
}
}
}
"""
**Don't Do This:**
"""typescript
// api-client.ts (Anti-pattern: Hardcoded API endpoint)
export class DefaultAPIClient {
async fetchData(): Promise {
const response = await fetch('https://api.example.com/api/data'); // Hardcoded URL
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
}
}
"""
### 1.3. Error Handling Strategy
**Standard:** Implement a consistent and centralized error handling mechanism for API calls. Use try/catch blocks and custom error classes.
**Why:** Provides a predictable way to handle API failures, improving debugging and enhancing user experience (e.g., showing appropriate error messages).
**Do This:**
"""typescript
// api-client.ts
export class APIError extends Error {
constructor(message: string, public statusCode: number) {
super(message);
this.name = 'APIError';
}
}
export class DefaultAPIClient {
async fetchData(endpoint: string): Promise {
try {
const response = await fetch(endpoint);
if (!response.ok) {
throw new APIError("HTTP error! status: ${response.status}", response.status);
}
return await response.json();
} catch (error: any) { // Explicit 'any' type for error
// Log the error, potentially with more context
console.error('API call failed:', error);
throw error; // Re-throw to propagate the error
}
}
}
// service.ts
import { APIError } from './api-client';
export class MyService {
async getData(): Promise {
try {
return await this.apiClient.fetchData('/api/data');
} catch (error) {
if (error instanceof APIError) {
console.error("API Error: ${error.message}, Status Code: ${error.statusCode}");
// Handle specific API errors (e.g., display user-friendly message)
} else {
console.error('Unexpected error:', error);
// Handle unexpected errors
}
throw error; // Re-throw or handle as needed
}
}
}
"""
**Don't Do This:**
"""typescript
// api-client.ts (Anti-pattern: Ignoring errors)
export class DefaultAPIClient {
async fetchData(endpoint: string): Promise {
try {
const response = await fetch(endpoint);
return await response.json(); // No error checking, potential crash
} catch (error) {
console.error("Error fetching data"); //Logging, but program continues as if nothing happened
return null; //This is a very bad practice
}
}
}
"""
### 1.4. Data Transformation
**Standard:** Implement data transformation and mapping logic to adapt API responses to the application's data models.
**Why:** Decouples the application from API-specific data structures, improving flexibility and maintainability.
**Do This:**
"""typescript
// api-client.ts
export interface RawUserData {
id: number;
firstName: string;
lastName: string;
emailAddress: string;
}
// models.ts
export interface User {
id: number;
fullName: string;
email: string;
}
// api-client.ts
export class DefaultAPIClient {
async fetchData(endpoint: string): Promise {
const response = await fetch(endpoint);
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
}
}
// service.ts
import {DefaultAPIClient, RawUserData} from './api-client';
import {User} from './models';
export class UserService {
constructor(private apiClient: DefaultAPIClient) {}
async getUsers(): Promise {
const rawUsers: RawUserData[] = await this.apiClient.fetchData('/api/users');
return rawUsers.map(this.transformUser);
}
private transformUser(rawUser: RawUserData): User {
return {
id: rawUser.id,
fullName: "${rawUser.firstName} ${rawUser.lastName}",
email: rawUser.emailAddress,
};
}
}
"""
**Don't Do This:**
"""typescript
// service.ts (Anti-pattern: Direct use of API data structures)
interface RawUserData { //Defined inside the service; tight coupling
id: number;
firstName: string;
lastName: string;
emailAddress: string;
}
export class MyService {
async getData(): Promise {
const response = await await fetch('/api/users');
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
}
}
"""
## 2. Implementation Details
### 2.1. Using "fetch" API
**Standard:** Use the native "fetch" API or a library built on top of it (e.g., "axios") for making HTTP requests. Configure request timeouts and handle abort signals.
**Why:** "fetch" is the standard API for making web requests, is supported natively in modern browsers/Node.js, and offers a cleaner interface compared to older methods like "XMLHttpRequest".
**Do This:**
"""typescript
// api-client.ts
import { API_CONFIG } from './config';
export class DefaultAPIClient {
async fetchData(endpoint: string): Promise {
const controller = new AbortController();
const timeoutId = setTimeout(() => controller.abort(), API_CONFIG.timeout);
try {
const response = await fetch("${API_CONFIG.baseURL}${endpoint}", {
signal: controller.signal, // Pass the abort signal
});
clearTimeout(timeoutId); // Clear timeout if request completes
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
} catch (error: any) {
clearTimeout(timeoutId); //clear timeout if abort happens
console.error('Fetch error:', error);
if (error.name === 'AbortError') {
console.log('Request aborted due to timeout.');
}
throw error;
}
}
}
"""
**Don't Do This:**
"""typescript
// api-client.ts (Anti-pattern: Using deprecated XMLHttpRequest)
export class DefaultAPIClient {
fetchData(endpoint: string): Promise {
return new Promise((resolve, reject) => {
const xhr = new XMLHttpRequest();
xhr.open('GET', endpoint);
xhr.onload = () => {
if (xhr.status >= 200 && xhr.status < 300) {
resolve(JSON.parse(xhr.responseText));
} else {
reject(new Error("Request failed with status: ${xhr.status}"));
}
};
xhr.onerror = () => reject(new Error('Network error'));
xhr.send();
});
}
}
"""
### 2.2. Data Serialization and Deserialization
**Standard:** Use "JSON.stringify" and "JSON.parse" for serializing and deserializing data when interacting with JSON APIs. Consider using libraries like "class-transformer" for complex object mapping.
**Why:** Ensures proper data formatting during API interactions. Advanced libraries provide features like type validation and custom transformation logic.
**Do This:**
"""typescript
// Example with JSON.stringify and JSON.parse
interface UserData {
name: string;
age: number;
}
async function postData(url: string, data: UserData): Promise {
const response = await fetch(url, {
method: 'POST',
headers: {
'Content-Type': 'application/json',
},
body: JSON.stringify(data),
});
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json(); // Assuming the response is also JSON
}
"""
For more complex cases, consider "class-transformer" (install with "npm install class-transformer class-validator --save")
"""typescript
import { plainToClass } from 'class-transformer';
import { validate } from 'class-validator';
class User {
id: number;
firstName: string;
lastName: string;
email: string;
}
async function fetchUser(url: string): Promise {
const response = await fetch(url);
const data = await response.json();
const user = plainToClass(User, data);
const errors = await validate(user); //Needs decorators on the class
if (errors.length > 0) {
console.error("Validation failed:", errors);
throw new Error("User data validation failed");
}
return user;
}
"""
**Don't Do This:**
"""typescript
// Anti-pattern: Manually constructing JSON strings (error-prone)
const data = { name: 'John', age: 30 };
const body = '{ "name": "' + data.name + '", "age": ' + data.age + ' }'; // Avoid this!
"""
### 2.3. Handling Authentication and Authorization
**Standard:** Implement secure authentication and authorization mechanisms (e.g., JWT, OAuth 2.0) for accessing protected APIs. Store credentials safely (e.g., using environment variables or secure storage). Use HTTPS for all API communications.
**Why:** Protects sensitive data and ensures that only authorized users/applications can access specific resources.
**Do This:**
"""typescript
// Example using JWT (JSON Web Token) in API client
import { API_CONFIG } from './config';
export class DefaultAPIClient {
private authToken: string | null = null;
setAuthToken(token: string): void {
this.authToken = token;
}
async fetchData(endpoint: string): Promise {
const headers: HeadersInit = {
'Content-Type': 'application/json',
// Add authentication token if available
};
if (this.authToken) {
headers['Authorization'] = "Bearer ${this.authToken}";
}
const response = await fetch("${API_CONFIG.baseURL}${endpoint}", {
headers,
});
if (!response.ok) {
if (response.status === 401) {
// Handle unauthorized error (e.g., redirect to login)
console.error("Unauthorized access, redirecting to login");
//Example: window.location.href = '/login';
}
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
}
}
//Example usage by service:
export class AuthService {
constructor(private apiClient: DefaultAPIClient){}
async login(credentials: Credentials): Promise {
const response = await fetch('/api/login', {
method: "POST",
body: JSON.stringify(credentials)
});
const body = await response.json();
if(response.ok && body.token){
this.apiClient.setAuthToken(body.token);
return true;
}
return false;
}
}
"""
**Don't Do This:**
"""typescript
// Anti-pattern: Storing API keys directly in the code (security risk)
const apiKey = 'YOUR_API_KEY'; //Never do this!
"""
### 2.4. Caching Strategies
**Standard:** Implement caching mechanisms to reduce the number of API calls and improve performance (e.g., using browser caching, service worker caching, or server-side caching).
**Why:** Reduces latency and improves responsiveness by serving data from cache instead of making frequent API requests.
**Do This (browser caching):**
"""typescript
// Setting cache headers on the server (Node.js example)
import express, { Request, Response } from 'express';
const app = express();
app.get('/api/data', (req: Request, res: Response) => {
// Set cache headers
res.set('Cache-Control', 'public, max-age=3600'); // Cache for 1 hour
res.json({ data: 'Cached data' });
});
"""
**Do This (Service Worker caching):**
This example shows a simple caching strategy within a service worker to cache API responses. This service worker would need to be setup within your application.
"""typescript
//In service-worker.js:
const CACHE_NAME = 'api-cache-v1';
const API_URL_REGEX = /^\/api\//; // Regex for API endpoints
self.addEventListener('install', (event: any) => {
console.log("Installing service worker");
event.waitUntil(
caches.open(CACHE_NAME).then(cache => {
//Cache static assets (optional)
return cache.addAll(['/', '/index.html', '/styles.css', '/script.js']);
})
);
});
self.addEventListener('fetch', (event: any) => {
const url = new URL(event.request.url);
if (url.origin === location.origin && API_URL_REGEX.test(url.pathname)) {
event.respondWith(
caches.match(event.request).then(response => {
//Return cached response if available
if(response) {
console.log("Returning cached response for:", event.request.url);
return response;
}
//Otherwise fetch from network, cache, and return
return fetch(event.request).then(networkResponse => {
if(!networkResponse || networkResponse.status !==200 || networkResponse.type !== 'basic'){
return networkResponse; //Don't cache if not a "good" response
}
const responseToCache = networkResponse.clone(); //Clone as response body can only be read once
caches.open(CACHE_NAME).then(cache => {
cache.put(event.request, responseToCache);
});
return networkResponse;
});
})
);
}
});
"""
**Don't Do This:**
"""typescript
// Anti-pattern: Never caching API responses (performance bottleneck)
"""
### 2.5. Rate Limiting
**Standard:** Implement rate limiting on the client-side to prevent overwhelming APIs with excessive requests.
**Why:** Avoids exceeding API usage limits and ensures fair access to resources, improving overall application stability.
**Do This:**
"""typescript
// Example using a basic rate limiter
class RateLimiter {
private calls: number = 0;
private lastReset: number = Date.now();
private maxCalls: number = 10;
private resetInterval: number = 60000; // 1 minute
canMakeCall(): boolean {
const now = Date.now();
if (now - this.lastReset > this.resetInterval) {
this.calls = 0;
this.lastReset = now;
}
return this.calls < this.maxCalls;
}
recordCall(): void {
this.calls++;
}
}
const limiter = new RateLimiter();
async function fetchDataWithRateLimit(url: string): Promise {
if (limiter.canMakeCall()) {
limiter.recordCall();
const response = await fetch(url);
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
} else {
throw new Error('Rate limit exceeded. Please try again later.');
}
}
// Usage
fetchDataWithRateLimit('/api/data')
.then(data => console.log(data))
.catch(error => console.error(error));
"""
**Don't Do This:**
"""typescript
// Anti-pattern: Making API calls in rapid succession without any rate limiting
"""
## 3. Asynchronous Operations
### 3.1. Using "async/await"
**Standard:** Use "async/await" syntax for handling asynchronous operations (e.g., API calls).
**Why:** Provides a more readable and maintainable way to write asynchronous code compared to callbacks or promises.
**Do This:**
"""typescript
async function fetchData(): Promise {
try {
const response = await fetch('/api/data');
if (!response.ok) {
throw new Error("HTTP error! status: ${response.status}");
}
return await response.json();
} catch (error: any) {
console.error('Fetch error:', error);
throw error; // Re-throw for handling in the calling function
}
}
"""
**Don't Do This:**
"""typescript
// Anti-pattern: Using nested callbacks (callback hell)
function fetchData(callback: (data: any) => void) {
fetch('/api/data')
.then(response => response.json())
.then(data => callback(data))
.catch(error => console.error(error));
}
"""
### 3.2. Parallel API Calls
**Standard:** Use "Promise.all" or "Promise.allSettled" to make multiple API calls in parallel when appropriate.
**Why:** Improves performance by reducing the overall time required to fetch data from multiple sources.
**Do This:**
"""typescript
async function fetchMultipleData(): Promise {
try {
const [data1, data2] = await Promise.all([
fetch('/api/data1').then(response => response.json()),
fetch('/api/data2').then(response => response.json()),
]);
return [data1, data2];
} catch (error: any) {
console.error('Error fetching data:', error);
return []; // Or handle error appropriately
}
}
"""
**Don't Do This:**
"""typescript
// Anti-pattern: Making API calls sequentially (slower performance)
async function fetchMultipleData(): Promise {
const data1 = await fetch('/api/data1').then(response => response.json());
const data2 = await fetch('/api/data2').then(response => response.json());
return [data1, data2];
}
"""
## 4. Data Validation
### 4.1. Input Validation
**Standard:** Validate user inputs and API request parameters to prevent injection attacks and ensure data integrity. Use libraries like "zod" or "yup" for schema validation.
**Why:** Enhances security by preventing malicious data from being sent to the API and ensures that the application receives valid data.
**Do This (using Zod):**
First, install Zod: "npm install zod"
"""typescript
import { z } from 'zod';
const UserSchema = z.object({
id: z.number().positive(),
username: z.string().min(3).max(20),
email: z.string().email(),
});
type User = z.infer;
async function createUser(userData: unknown): Promise {
try {
const parsedData = UserSchema.parse(userData);
// Send parsedData to the API
console.log('Valid user data:', parsedData);
return parsedData;
} catch (error: any) {
console.error('Validation error:', error.errors);
throw new Error('Invalid user data');
}
}
// Usage
const validUserData = {
id: 1,
username: 'johndoe',
email: 'john.doe@example.com',
};
const invalidUserData = {
id: -1,
username: 'jd',
email: 'invalid-email',
};
createUser(validUserData)
.then(user => console.log('Created user:', user))
.catch(error => console.error('Failed to create user:', error.message));
createUser(invalidUserData)
.catch(error => console.error('Failed to create user:', error.message));
"""
**Don't Do This:**
"""typescript
// Anti-pattern: Directly passing user input to the API without validation
async function createUser(username: string, email: string): Promise {
const response = await fetch('/api/users', {
method: 'POST',
body: JSON.stringify({ username, email }), //No validation!
});
return response.json();
}
"""
### 4.2. Response Validation
**Standard:** Validate API responses to ensure data consistency and handle unexpected data formats. Use TypeScript interfaces/types and runtime validation (e.g., with "zod") to ensure data conforms to expected schemas.
**Why:** Enhances robustness by preventing errors caused by malformed or unexpected API responses.
**Do This**:
"""typescript
import { z } from 'zod';
const ApiResponseSchema = z.object({
status: z.string(),
data: z.array(z.object({
id: z.number(),
name: z.string()
}))
});
type ApiResponse = z.infer;
async function fetchData(url: string) {
const response = await fetch(url);
const data = await response.json();
try {
const validatedData = ApiResponseSchema.parse(data);
console.log("Validated data:", validatedData);
return validatedData;
} catch (error) {
console.error("Response validation failed:", error);
throw error;
}
}
"""
**Don't Do This:**
"""typescript
// Anti-pattern: Assuming API responses are always in the expected format
async function fetchData(): Promise {
const response = await fetch('/api/data');
const data = await response.json();
return data.items; // Assuming data.items always exists and is an array!
}
"""
## 5. Testing
### 5.1. Unit Testing
**Standard:** Write unit tests for API client and service classes to ensure they function correctly. Mock API dependencies using libraries like "jest" or "sinon".
**Why:** Improves code quality by verifying functionality and preventing regressions during refactoring.
**Do This:**
"""typescript
// api-client.test.ts
import { DefaultAPIClient } from './api-client';
describe('DefaultAPIClient', () => {
it('should fetch data successfully', async () => {
const mockFetch = jest.fn().mockResolvedValue({
ok: true,
json: () => Promise.resolve({ data: 'test data' }),
});
global.fetch = mockFetch; // Mock the global fetch
const apiClient = new DefaultAPIClient();
const data = await apiClient.fetchData('/api/data');
expect(mockFetch).toHaveBeenCalledWith('/api/data');
expect(data).toEqual({ data: 'test data' });
});
it('should handle errors when fetching data', async () => {
const mockFetch = jest.fn().mockResolvedValue({
ok: false,
status: 500,
});
global.fetch = mockFetch;
const apiClient = new DefaultAPIClient();
await expect(apiClient.fetchData('/api/data')).rejects.toThrow('HTTP error! status: 500');
});
});
"""
**Don't Do This:**
"""typescript
// Anti-pattern: No unit tests for API interaction logic
"""
### 5.2. Integration Testing
**Standard:** Write integration tests to verify the interaction between different components and the API.
**Why:** Ensures that components work together correctly and the API integration functions as expected in a real-world scenario. These would likely utilize live dockerized APIs or mock servers running locally.
**Do This:**
The specific style would vary heavily depending on project setup so a simple example is not feasible in this document.
**Don't Do This:**
"""typescript
// Anti-pattern: Skipping integration tests and relying solely on unit tests
"""
By adhering to these standards, TypeScript developers can create robust, efficient, and maintainable API integrations. This document serves as a guideline for best practices, promoting consistency and quality across projects.
danielsogl
Created Mar 6, 2025
This guide explains how to effectively use .clinerules with Cline, the AI-powered coding assistant.
The .clinerules file is a powerful configuration file that helps Cline understand your project's requirements, coding standards, and constraints. When placed in your project's root directory, it automatically guides Cline's behavior and ensures consistency across your codebase.
Place the .clinerules file in your project's root directory. Cline automatically detects and follows these rules for all files within the project.
# Project Overview project: name: 'Your Project Name' description: 'Brief project description' stack: - technology: 'Framework/Language' version: 'X.Y.Z' - technology: 'Database' version: 'X.Y.Z'
# Code Standards standards: style: - 'Use consistent indentation (2 spaces)' - 'Follow language-specific naming conventions' documentation: - 'Include JSDoc comments for all functions' - 'Maintain up-to-date README files' testing: - 'Write unit tests for all new features' - 'Maintain minimum 80% code coverage'
# Security Guidelines security: authentication: - 'Implement proper token validation' - 'Use environment variables for secrets' dataProtection: - 'Sanitize all user inputs' - 'Implement proper error handling'
Be Specific
Maintain Organization
Regular Updates
# Common Patterns Example patterns: components: - pattern: 'Use functional components by default' - pattern: 'Implement error boundaries for component trees' stateManagement: - pattern: 'Use React Query for server state' - pattern: 'Implement proper loading states'
Commit the Rules
.clinerules in version controlTeam Collaboration
Rules Not Being Applied
Conflicting Rules
Performance Considerations
# Basic .clinerules Example project: name: 'Web Application' type: 'Next.js Frontend' standards: - 'Use TypeScript for all new code' - 'Follow React best practices' - 'Implement proper error handling' testing: unit: - 'Jest for unit tests' - 'React Testing Library for components' e2e: - 'Cypress for end-to-end testing' documentation: required: - 'README.md in each major directory' - 'JSDoc comments for public APIs' - 'Changelog updates for all changes'
# Advanced .clinerules Example project: name: 'Enterprise Application' compliance: - 'GDPR requirements' - 'WCAG 2.1 AA accessibility' architecture: patterns: - 'Clean Architecture principles' - 'Domain-Driven Design concepts' security: requirements: - 'OAuth 2.0 authentication' - 'Rate limiting on all APIs' - 'Input validation with Zod'
# TypeScript Performance Optimization Standards: Best Practices for Efficient Applications This document outlines coding standards and best practices specifically for performance optimization in TypeScript projects. Adhering to these guidelines will improve the speed, responsiveness, efficient use of resources, and overall user experience of your applications. ## Table of Contents - [1. Architectural Considerations for Performance](#1-architectural-considerations-for-performance) - [1.1. Code Splitting](#11-code-splitting) - [1.2. Lazy Loading Modules](#12-lazy-loading-modules) - [1.3. Server-Side Rendering (SSR) or Static Site Generation (SSG)](#13-server-side-rendering-ssr-or-static-site-generation-ssg) - [1.4. Data Structure Selection](#14-data-structure-selection) ## 1. Architectural Considerations for Performance ### 1.1. Code Splitting **Standard:** Implement code splitting to reduce the initial load time of your application. **Why:** Loading only the necessary code on initial page load significantly improves the user experience. **Do This:** * Utilize dynamic imports (`import()`) to load modules on demand. * Configure your bundler (Webpack, Parcel, Rollup) to create separate chunks for different parts of your application. **Don't Do This:** * Load the entire application code in a single bundle. * Use `require()` statements (CommonJS) in modern TypeScript projects where ES Modules are supported. **Example:** ```typescript // Before: Loading everything upfront import { featureA } from './featureA'; import { featureB } from './featureB'; // After: Code splitting with dynamic imports async function loadFeatureA() { const { featureA } = await import('./featureA'); featureA.init(); } async function loadFeatureB() { const { featureB } = await import('./featureB'); featureB.init(); } // Use loadFeatureA or loadFeatureB based on user interaction or route ``` **Bundler Configuration (Webpack example):** ```javascript // webpack.config.js module.exports = { entry: './src/index.ts', output: { filename: '[name].bundle.js', path: path.resolve(__dirname, 'dist'), }, module: { rules: [ { test: /\.tsx?$/, use: 'ts-loader', exclude: /node_modules/, }, ], }, resolve: { extensions: ['.tsx', '.ts', '.js'], }, optimization: { splitChunks: { chunks: 'all', // Split all chunks of code }, }, }; ``` ### 1.2. Lazy Loading Modules **Standard:** Employ lazy loading for non-critical modules or components. **Why:** Reduce the amount of code that needs to be parsed and compiled on initial load. **Do This:** * Load components or modules only when they are needed. * Utilize Intersection Observer API to load components when they become visible in the viewport. **Don't Do This:** * Load modules that are not immediately required for the current user interaction. **Example (Intersection Observer Lazy Loading):** ```typescript function lazyLoadComponent(element: HTMLElement, importPath: string) { const observer = new IntersectionObserver((entries) => { entries.forEach(async (entry) => { if (entry.isIntersecting) { const { default: Component } = await import(importPath); const componentInstance = new Component(); // Instantiate the component. element.appendChild(componentInstance.render()); // Append to the DOM (adjust according to your framework). observer.unobserve(element); } }); }); observer.observe(element); } // Usage: const lazyComponentElement = document.getElementById('lazy-component'); if (lazyComponentElement) { lazyLoadComponent(lazyComponentElement, './MyHeavyComponent'); } ``` ### 1.3. Server-Side Rendering (SSR) or Static Site Generation (SSG) **Standard:** Consider using SSR or SSG for content-heavy, SEO-sensitive, or performance-critical applications. **Why:** Reduces the time to first paint (TTFP) and improves SEO by providing crawlers with pre-rendered content. **Do This:** * Evaluate the trade-offs between SSR, SSG, and client-side rendering (CSR) based on your application's needs. * Use frameworks like Next.js (React), Nuxt.js (Vue), or Angular Universal. * Implement appropriate caching strategies for SSR. **Don't Do This:** * Default to CSR when SSR or SSG could provide significant performance benefits. **Example (Next.js):** ```typescript // pages/index.tsx (Next.js example) import React from 'react'; interface Props { data: { title: string; description: string; }; } const HomePage: React.FC<Props> = ({ data }) => { return ( <div> <h1>{data.title}</h1> <p>{data.description}</p> </div> ); }; export async function getServerSideProps() { // Fetch data from an API, database, or file system. const data = { title: 'My Awesome Website', description: 'Welcome to my extremely performant website!', }; return { props: { data, }, }; } export default HomePage; ``` ### 1.4. Data Structure Selection **Standard:** Select the most appropriate data structure for each specific use case. **Why:** Using appropriate data structures will reduce the complexity and improve the execution speed of algorithms. **Do This:** * Use `Map` when you need to associate keys with values, especially when the keys are not strings or numbers. * Use `Set` when you need to store a collection of unique values. * Use `Record<K, V>` type for type-safe object mapping. * Consider specialized data structures for specific performance needs (e.g., priority queues, linked lists). **Don't Do This:** * Use generic arrays or objects when more specialized data structures would be more efficient. * Perform frequent lookups in arrays when using a Map or Set would be more performant. **Example:** ```typescript // Before: Using an array for lookups const users = [ { id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }, { id: 3, name: 'Charlie' } ]; // O(n) lookup operation const findUser = (id: number) => users.find(user => user.id === id); // After: Using Map for efficient lookups const userMap = new Map<number, {id: number, name: string}>(); userMap.set(1, { id: 1, name: 'Alice' }); userMap.set(2, { id: 2, name: 'Bob' }); userMap.set(3, { id: 3, name: 'Charlie' }); // O(1) lookup operation const getUser = (id: number) => userMap.get(id); ```
Debe preferir usar el gestor de versiones "pnpm" por sobre "npm" para la ejecución de los comandos.
# Storybook Guidelines for Angular (v9.0.18+) Use these guidelines when working with Storybook in Angular projects. This document covers modern patterns, best practices, and the latest features in Storybook 9.x. ## 1. Core Architecture & Setup ### Framework Configuration - **Angular Framework**: Always use `@storybook/angular` as the framework in your `.storybook/main.ts` - **TypeScript First**: All configuration files should use TypeScript (`.ts` extension) - **Standalone Components**: Leverage Angular standalone components in stories - they work seamlessly with Storybook - **Modern Angular Patterns**: Support for Angular 17+ features including signals, control flow, and standalone APIs ### Basic Configuration Structure ```typescript // .storybook/main.ts import type { StorybookConfig } from '@storybook/angular'; const config: StorybookConfig = { framework: { name: '@storybook/angular', options: { // Framework-specific options }, }, stories: ['../src/**/*.stories.@(js|jsx|mjs|ts|tsx)'], addons: [ '@storybook/addon-essentials', '@storybook/addon-interactions', '@storybook/addon-a11y', '@storybook/addon-docs', '@storybook/addon-vitest', // For Storybook 9.x testing ], }; export default config; ``` ## 2. Story Structure & CSF 3 Patterns ### Modern Story Format (CSF 3) - **Component Story Format 3**: Use the latest CSF 3 syntax for all new stories - **TypeScript Types**: Always use `Meta` and `StoryObj` for type safety - **Minimal Boilerplate**: Leverage CSF 3's simplified syntax ```typescript import type { Meta, StoryObj } from '@storybook/angular'; import { Button } from './button.component'; const meta: Meta = { component: Button, }; export default meta; type Story = StoryObj; export const Primary: Story = { args: { primary: true, label: 'Button', }, }; export const Secondary: Story = { args: { primary: false, label: 'Button', }, }; ``` ### Story Naming & Organization - **Descriptive Names**: Use clear, descriptive names for story exports - **Hierarchical Titles**: Organize stories with meaningful hierarchies using forward slashes - **Auto-Generated Titles**: Leverage automatic title generation when possible - **Component-Centric**: Group stories by component, not by state ```typescript const meta: Meta = { title: 'Design System/Components/Button', // Hierarchical organization component: Button, }; ``` ## 3. Angular-Specific Patterns ### Standalone Components (Recommended) - **Default Approach**: Prefer standalone components for new development - **No Module Imports**: Avoid importing CommonModule or other NgModules - **Direct Dependencies**: Import only required standalone components, directives, or pipes ```typescript // ✅ Good - Standalone component story import type { Meta, StoryObj } from '@storybook/angular'; import { MyStandaloneComponent } from './my-standalone.component'; const meta: Meta = { component: MyStandaloneComponent, }; ``` ### Legacy Module-Based Components - **Module Metadata**: Use `moduleMetadata` decorator for components requiring NgModules - **Minimal Imports**: Import only necessary modules and declarations ```typescript // For legacy components requiring modules import { moduleMetadata } from '@storybook/angular'; import { CommonModule } from '@angular/common'; const meta: Meta = { component: LegacyComponent, decorators: [ moduleMetadata({ imports: [CommonModule], declarations: [LegacyComponent, ChildComponent], }), ], }; ``` ### Application Configuration - **Provider Setup**: Use `applicationConfig` decorator for dependency injection - **Service Mocking**: Configure providers for testing scenarios ```typescript import { applicationConfig } from '@storybook/angular'; import { importProvidersFrom } from '@angular/core'; import { BrowserAnimationsModule } from '@angular/platform-browser/animations'; const meta: Meta = { component: MyComponent, decorators: [ applicationConfig({ providers: [ importProvidersFrom(BrowserAnimationsModule), // Add other providers as needed ], }), ], }; ``` ## 4. Story Configuration & Best Practices ### Args and Controls - **Typed Args**: Leverage TypeScript for type-safe arguments - **Meaningful Defaults**: Provide sensible default values - **Control Types**: Explicitly define control types when needed ```typescript const meta: Meta = { component: Button, argTypes: { size: { control: { type: 'select' }, options: ['small', 'medium', 'large'], }, disabled: { control: { type: 'boolean' }, }, }, args: { // Default args for all stories size: 'medium', disabled: false, label: 'Button', }, }; ``` ### Parameters Configuration - **Global Parameters**: Set common parameters at the meta level - **Story-Specific Overrides**: Override parameters for specific stories when needed - **Documentation**: Use parameters for docs configuration ```typescript const meta: Meta = { component: Button, parameters: { docs: { description: { component: 'A versatile button component for user interactions.', }, }, backgrounds: { default: 'light', }, }, }; export const OnDark: Story = { parameters: { backgrounds: { default: 'dark' }, }, }; ``` ## 5. Advanced Patterns ### Custom Render Functions - **Complex Templates**: Use render functions for complex component templates - **Template Customization**: Provide custom templates when component alone isn't sufficient ```typescript export const WithCustomTemplate: Story = { render: args => ({ props: args, template: ` <p>Additional content around the button</p> `, }), }; ``` ### Component Composition - **Multi-Component Stories**: Show components working together - **Real-World Scenarios**: Create stories that demonstrate actual usage patterns ```typescript const meta: Meta = { component: List, decorators: [ moduleMetadata({ declarations: [List, ListItem], }), ], }; export const WithItems: Story = { render: args => ({ props: args, template: ` Item 1 Item 2 Item 3 `, }), }; ``` ## 6. Testing Integration (Storybook 9.x) ### Vitest Addon Integration - **Modern Testing**: Use `@storybook/addon-vitest` for component testing - **Story-Based Tests**: Transform stories into tests automatically - **Browser Mode**: Leverage Vitest's browser mode for realistic testing ```bash # Install and configure Vitest addon npx storybook@latest add @storybook/addon-vitest ``` ### Interaction Testing - **Play Functions**: Use play functions for interaction testing - **User Events**: Simulate real user interactions - **Assertions**: Include meaningful assertions in play functions ```typescript import { userEvent, within, expect } from '@storybook/test'; export const InteractiveTest: Story = { args: { label: 'Click me', }, play: async ({ canvasElement }) => { const canvas = within(canvasElement); const button = canvas.getByRole('button'); await userEvent.click(button); await expect(button).toHaveClass('clicked'); }, }; ``` ### Accessibility Testing - **A11y Addon**: Include `@storybook/addon-a11y` for accessibility checks - **ARIA Labels**: Ensure proper ARIA labeling in stories - **Keyboard Navigation**: Test keyboard accessibility ```typescript const meta: Meta = { component: Button, parameters: { a11y: { config: { rules: [ { id: 'color-contrast', enabled: true, }, ], }, }, }, }; ``` ## 7. Documentation & Docs Integration ### Compodoc Integration - **API Documentation**: Integrate Compodoc for automatic API docs generation - **Angular.json Configuration**: Configure builders for Compodoc integration ```json // angular.json { "projects": { "your-project": { "architect": { "storybook": { "builder": "@storybook/angular:start-storybook", "options": { "compodoc": true, "compodocArgs": ["-e", "json", "-d", "."] } } } } } } ``` ```typescript // .storybook/preview.ts import { setCompodocJson } from '@storybook/addon-docs/angular'; import docJson from '../documentation.json'; setCompodocJson(docJson); ``` ### Story Documentation - **JSDoc Comments**: Use JSDoc comments for automatic documentation - **Description Parameters**: Override descriptions when needed - **Code Examples**: Include relevant code examples ```typescript /** * Primary button component for user actions. * Supports various sizes and states. */ const meta: Meta = { component: Button, parameters: { docs: { description: { component: 'The primary button component with full accessibility support.', }, }, }, }; /** * The primary button state - used for main actions */ export const Primary: Story = { parameters: { docs: { description: { story: 'Use this variant for primary actions like "Save" or "Submit".', }, }, }, }; ``` ## 8. Performance & Optimization ### Lazy Loading - **Code Splitting**: Leverage Angular's lazy loading for large component libraries - **Story Optimization**: Keep stories focused and lightweight - **Asset Management**: Optimize images and other assets ### Bundle Optimization - **Tree Shaking**: Ensure proper tree shaking of unused code - **Minimal Dependencies**: Import only necessary dependencies - **Build Configuration**: Optimize build configuration for production ## 9. Theming & Styling ### Angular Material Integration - **Theme Providers**: Use decorators to provide Angular Material themes - **Component Wrapper**: Wrap stories with theme providers when needed ```typescript import { componentWrapperDecorator } from '@storybook/angular'; const meta: Meta = { component: MyComponent, decorators: [componentWrapperDecorator(story => `${story}`)], }; ``` ### CSS Custom Properties - **Design Tokens**: Use CSS custom properties for consistent theming - **Theme Switching**: Implement theme switching in stories - **Responsive Design**: Test components across different viewports ## 10. File Organization & Naming ### File Structure - **Co-location**: Keep stories close to their components - **Consistent Naming**: Use consistent naming patterns - **Logical Grouping**: Group related stories together ``` src/ components/ button/ button.component.ts button.component.html button.component.scss button.component.stories.ts button.component.spec.ts ``` ### Naming Conventions - **Story Files**: Use `.stories.ts` extension - **Export Names**: Use PascalCase for story exports - **File Names**: Use kebab-case for file names ## 11. CI/CD Integration ### Build Configuration - **Static Builds**: Configure static build for deployment - **Environment Variables**: Handle environment-specific configuration - **Testing Pipeline**: Integrate story testing in CI/CD ```bash # Build Storybook for production ng run your-project:build-storybook # Run tests with Vitest addon npm run test-storybook ``` ### Deployment - **Static Hosting**: Deploy to static hosting services - **Version Management**: Tag releases with version numbers - **Documentation Updates**: Keep documentation in sync with code ## 12. Migration & Maintenance ### Upgrading Storybook - **Regular Updates**: Keep Storybook updated to latest versions - **Migration Guides**: Follow official migration guides - **Breaking Changes**: Test thoroughly after major updates ### Legacy Code Migration - **Gradual Migration**: Migrate stories incrementally - **CSF 2 to CSF 3**: Upgrade older story formats - **Module to Standalone**: Migrate to standalone components when possible ## 13. Common Patterns & Examples ### Form Components ```typescript export const FormExample: Story = { render: args => ({ props: args, template: ` `, }), }; ``` ### Data Loading States ```typescript export const Loading: Story = { args: { loading: true, data: null, }, }; export const WithData: Story = { args: { loading: false, data: mockData, }, }; export const Error: Story = { args: { loading: false, error: 'Failed to load data', }, }; ``` ### Responsive Components ```typescript export const Mobile: Story = { parameters: { viewport: { defaultViewport: 'mobile1', }, }, }; export const Desktop: Story = { parameters: { viewport: { defaultViewport: 'desktop', }, }, }; ``` ## 14. Quality Guidelines ### Code Quality - **TypeScript Strict Mode**: Use strict TypeScript configuration - **ESLint Rules**: Follow Storybook-specific ESLint rules - **Consistent Formatting**: Use Prettier for code formatting ### Testing Standards - **Coverage Goals**: Aim for high story coverage of component states - **Interaction Tests**: Include interaction tests for complex components - **Accessibility Tests**: Ensure all stories pass accessibility checks ### Documentation Standards - **Complete Coverage**: Document all component props and behaviors - **Real Examples**: Provide realistic usage examples - **Up-to-date**: Keep documentation synchronized with code changes ## 15. Troubleshooting & Common Issues ### Angular-Specific Issues - **Module Dependencies**: Ensure all required modules are imported - **Provider Configuration**: Check provider setup for dependency injection - **Change Detection**: Consider OnPush change detection strategy ### Performance Issues - **Bundle Size**: Monitor and optimize bundle size - **Memory Leaks**: Watch for memory leaks in complex stories - **Build Time**: Optimize build configuration for faster development This comprehensive guide ensures you're following the latest best practices for Storybook 9.x with Angular, leveraging modern features like the Vitest addon, improved testing capabilities, and optimized development workflows.
# Code Style and Conventions Standards for TypeScript This document outlines coding style and conventions standards for TypeScript development. Adhering to these standards promotes code consistency, readability, maintainability, and collaboration within development teams. These guidelines are tailored for the latest version of TypeScript and aim to leverage modern best practices. ## 1. Formatting Consistent formatting is crucial for readability. We adopt the following standards for TypeScript code formatting: ### 1.1. Whitespace and Indentation * **Standard:** Use 2 spaces for indentation. Avoid tabs. * **Why:** Consistent indentation enhances readability and reduces visual clutter. * **Do This:** """typescript function calculateArea(width: number, height: number): number { const area = width * height; return area; } """ * **Don't Do This:** """typescript function calculateArea(width: number, height: number): number { const area = width * height; return area; } """ * **Standard:** Use blank lines to separate logical sections of code within functions and classes. * **Why:** Separating logical blocks improves code comprehension. * **Do This:** """typescript function processData(data: any[]): void { // Validate data if (!data || data.length === 0) { throw new Error("Data is invalid."); } // Transform data const transformedData = data.map(item => ({ ...item, processed: true, })); // Save data saveToDatabase(transformedData); } """ ### 1.2. Line Length * **Standard:** Limit lines to a maximum of 120 characters. * **Why:** Enforces readability on various screen sizes and IDE configurations. * **How:** Configure your editor or IDE to display a line length guide at 120 characters. Break long lines at logical points, such as after commas, operators, or before opening parentheses. * **Do This:** """typescript const veryLongVariableName = calculateSomethingComplicated( param1, param2, param3 ); """ * **Don't Do This:** """typescript const veryLongVariableName = calculateSomethingComplicated(param1, param2, param3); """ ### 1.3. Braces and Parentheses * **Standard:** Use braces for all control flow statements, even single-line statements. * **Why:** Improves code clarity and reduces potential errors when modifying code. * **Do This:** """typescript if (isValid) { console.log("Valid"); } else { console.log("Invalid"); } """ * **Don't Do This:** """typescript if (isValid) console.log("Valid"); else console.log("Invalid"); """ * **Standard:** Use parentheses to clarify operator precedence, where needed. * **Why:** Reduces ambiguity, especially in complex expressions. * **Example:** """typescript const result = (a + b) * c; """ ### 1.4. Semicolons * **Standard:** Always use semicolons to terminate statements. * **Why:** Prevents unexpected behavior due to JavaScript's automatic semicolon insertion (ASI). * **Do This:** """typescript const name = "John"; console.log(name); """ * **Don't Do This:** """typescript const name = "John" console.log(name) """ ## 2. Naming Conventions Consistent naming conventions are essential for code clarity and maintainability. ### 2.1. Variables and Constants * **Standard:** Use camelCase for variable and constant names. * **Why:** Widely adopted convention for JavaScript and TypeScript. * **Do This:** """typescript const userName = "Alice"; let itemCount = 0; """ * **Standard:** Use UPPER_SNAKE_CASE for constant values (i.e. values that may be inlined for performance or are known at compile time). * **Why:** Clearly distinguishes constants from variables. * **Do This:** """typescript const MAX_RETRIES = 3; const API_ENDPOINT = "https://example.com/api"; """ ### 2.2. Functions and Methods * **Standard:** Use camelCase for function and method names. * **Why:** Follows common JavaScript/TypeScript conventions. * **Do This:** """typescript function calculateTotal(price: number, quantity: number): number { return price * quantity; } class ShoppingCart { addItem(item: string): void { console.log("Adding ${item} to the cart."); } } """ ### 2.3. Classes and Interfaces * **Standard:** Use PascalCase for class and interface names. * **Why:** Clearly identifies classes and interfaces. * **Do This:** """typescript interface User { id: number; name: string; } class Product { constructor(public name: string, public price: number) {} } """ ### 2.4. Type Parameters * **Standard:** Use single uppercase letters, typically "T", "U", "V", etc., for generic type parameters. * **Why:** Follows established TypeScript conventions. * **Do This:** """typescript function identity<T>(arg: T): T { return arg; } """ ### 2.5. Boolean Variables * **Standard:** Prefix boolean variables with "is", "has", or "should" to indicate a boolean value. * **Why:** Improves readability by clearly indicating the purpose of the variable. * **Do This:** """typescript let isValid: boolean = true; let hasPermission: boolean = false; let shouldUpdate: boolean = true; """ ## 3. Stylistic Consistency Consistency in style is critical for code maintainability. ### 3.1. Type Annotations and Inference * **Standard:** Use explicit type annotations where type inference is not obvious, especially for function parameters and return types. * **Why:** Improves code clarity and helps catch type-related errors early. * **Do This:** """typescript function greet(name: string): string { return "Hello, ${name}!"; } const add: (x: number, y: number) => number = (x, y) => x + y; """ * **Don't Do This:** """typescript function greet(name) { // Implicit 'any' type return "Hello, ${name}!"; } """ * **Standard:** Leverage type inference for local variables when the type is immediately apparent. * **Why:** Reduces verbosity and keeps code concise. * **Do This:** """typescript const message = "Hello, world!"; // Type inferred as string const count = 10; // Type inferred as number """ * **Standard:** When initializing variables with "null" or "undefined", explicitly define the type. * **Why:** Helps avoid unexpected type-related issues later. * **Do This:** """typescript let user: User | null = null; let data: string[] | undefined = undefined; """ ### 3.2. String Usage * **Standard:** Prefer template literals for string concatenation and multi-line strings. * **Why:** More readable and easier to maintain compared to traditional string concatenation. * **Do This:** """typescript const name = "Alice"; const message = "Hello, ${name}!"; const multiLine = "This is a multi-line string."; """ * **Don't Do This:** """typescript const name = "Alice"; const message = "Hello, " + name + "!"; const multiLine = "This is a\n" + "multi-line string."; """ ### 3.3. Object Literals * **Standard:** Use shorthand notation for object properties when the property name matches the variable name. * **Why:** Improves code conciseness and readability. * **Do This:** """typescript const name = "Alice"; const age = 30; const user = { name, age }; // Shorthand notation """ * **Don't Do This:** """typescript const name = "Alice"; const age = 30; const user = { name: name, age: age }; """ * **Standard:** Use object spread syntax for creating copies of objects or merging objects. * **Why:** More concise and readable than older methods like "Object.assign()". * **Do This:** """typescript const original = { a: 1, b: 2 }; const copy = { ...original, c: 3 }; // Creates a new object with a, b, and c """ ### 3.4. Arrow Functions * **Standard:** Use arrow functions for concise function expressions, especially for callbacks and inline functions. * **Why:** More compact syntax and lexically binds "this". * **Do This:** """typescript const numbers = [1, 2, 3]; const squared = numbers.map(x => x * x); // Concise arrow function """ * **Don't Do This:** """typescript const numbers = [1, 2, 3]; const squared = numbers.map(function(x) { return x * x; }); """ * **Standard:** Omit parentheses for single-parameter arrow functions. * **Why:** Makes the code even more concise. * **Do This:** """typescript const increment = x => x + 1; """ * **Don't Do This:** """typescript const increment = (x) => x + 1; """ ### 3.5. Modern TypeScript Features * **Standard:** Leverage features like optional chaining ("?.") and nullish coalescing ("??") for safer and more concise code. Optional properties on interfaces may be relevant if these are in use. * **Why:** Reduces boilerplate and improves null/undefined handling. * **Do This:** """typescript interface User { profile?: { address?: { city?: string; } } } const user: User = {}; const city = user?.profile?.address?.city ?? "Unknown"; // Nullish coalescing console.log(city); interface Config { timeout?: number; } const defaultConfig: Config = { timeout: 5000, }; function initialize(config?: Config) { const timeout = config?.timeout ?? defaultConfig.timeout; console.log("Timeout: ${timeout}"); } initialize(); // Timeout: 5000 initialize({ timeout: 10000 }); // Timeout: 10000 """ * **Standard:** Utilize discriminated unions and exhaustive checks for increased type safety and maintainability. * **Why:** Improves type correctness and makes it easier to handle different states or object types. * **Do This:** """typescript interface Success { type: "success"; result: any; } interface Error { type: "error"; message: string; } type Result = Success | Error; function handleResult(result: Result) { switch (result.type) { case "success": console.log("Success:", result.result); break; case "error": console.error("Error:", result.message); break; default: // Exhaustive check: TypeScript will flag this if a new type is added to Result const _exhaustiveCheck: never = result; return _exhaustiveCheck; } } const successResult: Success = { type: "success", result: { data: "example" } }; const errorResult: Error = { type: "error", message: "Something went wrong" }; handleResult(successResult); handleResult(errorResult); """ ### 3.6. Asynchronous Code * **Standard:** Always use "async/await" syntax for asynchronous operations. * **Why:** Improves readability and simplifies error handling compared to traditional promise chains. * **Do This:** """typescript async function fetchData(): Promise<any> { try { const response = await fetch("https://example.com/api/data"); const data = await response.json(); return data; } catch (error) { console.error("Error fetching data:", error); throw error; } } """ * **Don't Do This:** """typescript function fetchData(): Promise<any> { return fetch("https://example.com/api/data") .then(response => response.json()) .then(data => data) .catch(error => { console.error("Error fetching data:", error); throw error; }); } """ * **Standard:** Use "Promise.all" for concurrent asynchronous operations that don't depend on each other. * **Why:** Improves performance by executing asynchronous tasks in parallel. * **Do This:** """typescript async function processData(): Promise<void> { const [result1, result2] = await Promise.all([ fetchData1(), fetchData2(), ]); console.log("Result 1:", result1); console.log("Result 2:", result2); } """ ### 3.7 Error Handling * **Standard:** Implement robust error handling using "try...catch" blocks, especially in asynchronous functions. * **Why:** Prevents unhandled exceptions and allows for graceful recovery. * **Do This:** """typescript async function doSomething() { try { const result = await someAsyncOperation(); console.log("Result:", result); } catch (error) { console.error("An error occurred:", error); // Implement specific error handling/logging } } """ * **Standard:** Create custom error classes to provide more context and specify error handling logic. * **Why:** Extends the built-in Error to communicate more specific information about the error to the outside world. * **Do This:** """typescript class CustomError extends Error { constructor(message: string, public errorCode: number) { super(message); this.name = "CustomError"; Object.setPrototypeOf(this, CustomError.prototype); } } async function performOperation() { try { // some operation throw new CustomError("Operation failed", 500); } catch (error) { if (error instanceof CustomError) { console.error("Custom Error ${error.errorCode}: ${error.message}"); } else { console.error("An unexpected error occurred:", error); } } } """ ### 3.8 Immutability * **Standard:** Strive for immutability whenever practical, using "const" for variables that should not be reassigned and avoiding direct modification of objects and arrays. * **Why:** Makes code more predictable and easier to reason about, reducing the risk of bugs. * **Do This:** """typescript const originalArray = [1, 2, 3]; const newArray = [...originalArray, 4]; // Creates a new array const originalObject = { a: 1, b: 2 }; const newObject = { ...originalObject, c: 3 }; // Creates a new object """ * **Don't Do This:** """typescript const originalArray = [1, 2, 3]; originalArray.push(4); // Modifies the original array const originalObject = { a: 1, b: 2 }; originalObject.c = 3; // Modifies the original object """ ### 3.9 Comments * **Standard:** Add comments to explain complex or non-obvious logic, but prioritize writing self-documenting code. * **Why:** Comments should supplement, not replace, clear code. * **Guidelines:** * Use JSDoc-style comments for documenting functions, classes, and interfaces. * Explain the *why*, not the *what*. The code should explain what it does. * Keep comments concise and up-to-date. * Remove outdated or redundant comments. * **Example:** """typescript /** * Calculates the area of a rectangle. * @param width The width of the rectangle. * @param height The height of the rectangle. * @returns The area of the rectangle. */ function calculateArea(width: number, height: number): number { return width * height; } """ ## 4. Technology Specific Details (Distinguishing Good from Great) * **Standard:** Take advantage of TypeScript's advanced type features to create robust and maintainable code structures. * **Guidelines:** * **Utility Types:** Employ TypeScript's utility types ("Partial", "Readonly", "Pick", "Omit", "Record", etc.) to manipulate types and generate new types efficiently. """typescript interface User { id: number; name: string; email: string; age: number; } // Make all properties optional type PartialUser = Partial<User>; // Make specified properties required type RequiredIdAndName = Required<Pick<User, 'id' | 'name'>>; // Type with only certain properties type UserInfo = Pick<User, 'name' | 'email'>; // Type without certain properties type UserWithoutId = Omit<User, 'id'>; """ * **Mapped Types:** Utilize mapped types to transform the properties of an existing type, providing a dynamic way to define new types based on existing ones. """typescript interface Product { id: string; name: string; price: number; } // Create a read-only version of Product type ReadonlyProduct = Readonly<Product>; // Create a type where all properties of Product are nullable type NullableProduct = { [K in keyof Product]: Product[K] | null; }; """ * **Conditional Types:** Conditional types allow to define types based on conditions, adding yet another powerful layer of abstraction to type definitions. They help to ensure type safety throughout an application. """typescript type NonNullableProperty<T, K extends keyof T> = T[K] extends null | undefined ? never : K; type RequiredProperties<T> = Pick<T, NonNullableProperty<T, keyof T>>; interface Configuration { host?: string; port?: number; // Port can be potentially undefined or null timeout?: number; } // Extracts properties that are guaranteed to be assigned during runtime. type RuntimeProperties = RequiredProperties<Configuration>; // Result equivalent to {timeout: number;} """ * **Decorators:** Use decorators to add metadata or modify the behavior of classes, methods, properties, or parameters. * **Why:** Provide a declarative and reusable way to add functionality, such as logging, validation, or dependency injection. * **Example:** """typescript function logMethod(target: any, propertyKey: string, descriptor: PropertyDescriptor) { const originalMethod = descriptor.value; descriptor.value = function(...args: any[]) { console.log("Calling method ${propertyKey} with arguments: ${JSON.stringify(args)}"); const result = originalMethod.apply(this, args); console.log("Method ${propertyKey} returned: ${result}"); return result; }; return descriptor; } class Calculator { @logMethod add(a: number, b: number): number { return a + b; } } const calculator = new Calculator(); calculator.add(2, 3); // Output: // Calling method add with arguments: [2,3] // Method add returned: 5 """ ## 5. Tooling * **Standard:** Use Prettier for automatic code formatting and ESLint with recommended TypeScript rules for linting. * **Why:** Automates formatting and enforces code quality, reducing manual effort and improving consistency. * **Configuration:** Configure Prettier and ESLint to work seamlessly with your IDE and CI/CD pipeline. * **Example ".eslintrc.js" configuration:** """javascript module.exports = { parser: "@typescript-eslint/parser", parserOptions: { ecmaVersion: 2020, sourceType: "module", project: './tsconfig.json', }, plugins: ["@typescript-eslint"], extends: [ "eslint:recommended", "plugin:@typescript-eslint/recommended", "plugin:@typescript-eslint/recommended-requiring-type-checking", "prettier", ], rules: { // Add or override rules here }, }; """ By adhering to these coding standards, TypeScript projects will benefit from improved code quality, readability, and maintainability, fostering a collaborative and productive development environment.
# Core Architecture Standards for TypeScript This document outlines coding standards specifically for the core architecture of TypeScript projects. It focuses on fundamental architectural patterns, project structure, and organization principles essential for large, maintainable, and scalable TypeScript applications. ## 1. Architectural Patterns ### 1.1 Microservices Architecture **Standard:** When building large-scale applications, consider a microservices architecture. * **Do This:** Decompose the application into independent, deployable services. Each service should own a specific business domain. * **Don't Do This:** Create a monolithic application that combines disparate functionalities into a single codebase, leading to tightly coupled components and scalability bottlenecks. **Why:** Microservices enable independent scaling, deployment, and technology choices for different parts of the application, significantly boosting agility and resilience. **Code Example:** Illustrating a simple microservice interface """typescript // microservice-interface.ts export interface UserService { getUser(id: string): Promise<{ id: string; name: string; email: string }>; createUser(user: { name: string; email: string }): Promise<string>; } export class UserServiceClient implements UserService { private baseUrl: string; constructor(baseUrl: string) { this.baseUrl = baseUrl; } async getUser(id: string): Promise<{ id: string; name: string; email: string }> { const response = await fetch("${this.baseUrl}/users/${id}"); return response.json(); } async createUser(user: { name: string; email: string }): Promise<string> { const response = await fetch("${this.baseUrl}/users", { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify(user), }); const newUser = await response.json(); return newUser.id; } } """ ### 1.2 Layered Architecture **Standard:** Organize code into distinct layers (presentation, application, domain, infrastructure). * **Do This:** Separate concerns by grouping related functionality into loosely coupled layers. * **Don't Do This:** Mix presentation logic with business rules or database access code. **Why:** Layered architecture improves testability, maintainability, and reusability by isolating dependencies and responsibilities. **Code Example:** Layered approach to data handling with repositories """typescript // domain/user.ts export interface User { id: string; name: string; email: string; } // infrastructure/user-repository.ts import { User } from '../domain/user'; export interface UserRepository { getUserById(id: string): Promise<User | null>; saveUser(user: User): Promise<void>; } export class InMemoryUserRepository implements UserRepository { private users: { [id: string]: User } = {}; async getUserById(id: string): Promise<User | null> { return this.users[id] || null; } async saveUser(user: User): Promise<void> { this.users[user.id] = user; } } // application/user-service.ts import { UserRepository, InMemoryUserRepository } from '../infrastructure/user-repository'; import { User } from '../domain/user'; export class UserService { private userRepository: UserRepository; constructor(userRepository: UserRepository) { this.userRepository = userRepository; } async getUser(id: string): Promise<User | null> { return this.userRepository.getUserById(id); } async createUser(name: string, email: string): Promise<User> { const id = Math.random().toString(36).substring(2, 15); // generate a more robust ID for real applications const user: User = { id, name, email }; await this.userRepository.saveUser(user); return user; } } // presentation/user-controller.ts import { UserService } from '../application/user-service'; import { InMemoryUserRepository } from '../infrastructure/user-repository'; const userRepository = new InMemoryUserRepository(); const userService = new UserService(userRepository); async function main() { const newUser = await userService.createUser("John Doe", "john.doe@example.com"); const retrievedUser = await userService.getUser(newUser.id); console.log(retrievedUser); } main(); """ ### 1.3 Hexagonal Architecture (Ports and Adapters) **Standard:** Decouple the core business logic from external dependencies using ports and adapters. * **Do This:** Define interfaces (ports) for interacting with external systems (databases, APIs, UI). Implement adapters that translate between these interfaces and the specific technologies. * **Don't Do This:** Directly embed database queries or API calls within the core domain logic. **Why:** Hexagonal architecture makes it easier to switch technologies, test the core logic in isolation, and adapt to changing requirements. **Code Example:** Hexagonal Architecture using TypeScript interfaces & implementations """typescript // Interface -> Port interface PaymentGateway { processPayment(amount: number, creditCard: string): Promise<boolean>; } // Implementation -> Adapter for Stripe class StripePaymentGateway implements PaymentGateway { async processPayment(amount: number, creditCard: string): Promise<boolean> { // integrate with Stripe API here. For example: console.log("Processing $${amount} via Stripe with credit card ${creditCard}"); return true; // Simulated result } } // Implementation -> Adapter for PayPal class PayPalPaymentGateway implements PaymentGateway { async processPayment(amount: number, creditCard: string): Promise<boolean> { // integrate with PayPal API here console.log("Processing $${amount} via PayPal with credit card ${creditCard}"); return true; // Simulated result } } // Core Application Logic class PaymentService { private paymentGateway: PaymentGateway; constructor(paymentGateway: PaymentGateway) { this.paymentGateway = paymentGateway; } async charge(amount: number, creditCard: string): Promise<boolean> { return await this.paymentGateway.processPayment(amount, creditCard); } } // Usage: async function main() { const stripeGateway = new StripePaymentGateway(); const payPalGateway = new PayPalPaymentGateway(); const paymentServiceStripe = new PaymentService(stripeGateway); // Inject Stripe const paymentServicePayPal = new PaymentService(payPalGateway); // Inject PayPal const stripeResult = await paymentServiceStripe.charge(100, "1234-5678-9012-3456"); const paypalResult = await paymentServicePayPal.charge(50, "9876-5432-1098-7654"); console.log("Stripe Payment Result: ${stripeResult}"); console.log("PayPal Payment Result: ${paypalResult}"); } main(); """ ### 1.4 CQRS (Command Query Responsibility Segregation) **Standard:** Separate read operations (queries) from write operations (commands). * **Do This:** Define dedicated models and data access patterns for reading and writing data. * **Don't Do This:** Use the same data model and database queries for both reads and writes, potentially leading to performance issues and complex code. **Why:** CQRS allows optimizing read and write operations independently. This is particularly useful in scenarios with high read/write ratios. **Code Example:** Implementing CQRS pattern in TypeScript """typescript // Command: CreateUserCommand interface CreateUserCommand { type: 'CreateUser'; name: string; email: string; } // Query: GetUserQuery interface GetUserQuery { type: 'GetUser'; id: string; } // Command Handler class UserCommandHandler { async handle(command: CreateUserCommand): Promise<string> { if (command.type === 'CreateUser') { // Create user logic (e.g., save to database) const userId = Math.random().toString(36).substring(2, 15); console.log("Creating user with name ${command.name} and email ${command.email} (ID: ${userId})"); return userId // Return the new User ID } throw new Error('Invalid command'); } } // Query Handler class UserQueryHandler { async handle(query: GetUserQuery): Promise<{ id: string; name: string; email: string } | null > { if (query.type === 'GetUser') { // Retrieve user logic (e.g., fetch from database) console.log("Retrieving user with ID ${query.id}"); return { id: query.id, name: 'Example User', email: 'user@example.com' }; } throw new Error('Invalid query'); } } // Usage example: async function main() { const commandHandler = new UserCommandHandler(); const queryHandler = new UserQueryHandler(); const createUserCommand: CreateUserCommand = { type: 'CreateUser', name: 'John Doe', email: 'john.doe@example.com' }; const userId = await commandHandler.handle(createUserCommand); // creates a theoretical user console.log("User created with ID: ${userId}"); const getUserQuery: GetUserQuery = { type: 'GetUser', id: userId // Using the generated user ID }; const user = await queryHandler.handle(getUserQuery); if(user){ console.log("Retrieved user: ${JSON.stringify(user)}"); } else { console.log("User with ID ${getUserQuery.id} not found."); } } main(); """ ## 2. Project Structure and Organization ### 2.1 Modular File Structure **Standard:** Organize code into modules based on functionality, following a logical directory structure. * **Do This:** Group related files (components, services, interfaces) within dedicated directories. Use meaningful names for files and directories. Consider feature-based or layer-based structuring. * **Don't Do This:** Place all files in a single directory or create a folder structure that mirrors implementation details rather than business logic. **Why:** A modular structure improves code discoverability, maintainability, and collaboration among developers. """ src/ ├── components/ # Reusable UI components │ ├── button/ # Specific Button component │ │ ├── button.tsx # JSX code │ │ ├── button.module.css # Styles using CSS modules │ │ └── index.ts # Exports │ ├── input/ # Specific Input component │ │ ├── input.tsx # JSX code │ │ ├── input.module.css # Styles using CSS modules │ │ └── index.ts # Exports │ └── index.ts # Exports all reusable components ├── services/ # Business logic and API interactions │ ├── auth/ # Authentication-specific logic │ │ ├── auth-service.ts # Authentication service │ │ └── index.ts # Exports │ ├── api/ # API client │ │ ├── api-client.ts # API client │ │ └── index.ts # Exports │ └── index.ts # Exports all services ├── models/ # Data models / Types │ ├── user.ts # User model │ └── product.ts # Product model ├── utils/ # Utility functions │ ├── helper-functions.ts # Various utility functions │ └── index.ts # Exports ├── app.tsx # Main application component ├── styles/ # Global styles │ └── global.css ├── index.tsx # Entry point └── tsconfig.json # TypeScript configuration """ ### 2.2 Explicit Dependencies **Standard:** Declare all dependencies explicitly using "import" statements. * **Do This:** Import only the necessary modules or functions. Use named imports where possible. * **Don't Do This:** Rely on implicit global variables or wildcard imports ("import * as ..."). **Why:** Explicit dependencies allow for better code analysis, refactoring, and dependency management. **Code Example:** Named vs. wildcard imports """typescript // Good: Named imports import { useState, useEffect } from 'react'; import { calculateTotal } from './utils'; // Bad: Wildcard imports (less explicit) import * as React from 'react'; // Avoid unless necessary import * as Utils from './utils';// Avoid unless necessary """ ### 2.3 Single Responsibility Principle (SRP) **Standard:** Each module (class, function, component) should have one, and only one, reason to change. * **Do This:** Decompose complex functionalities into smaller, focused modules. * **Don't Do This:** Create "god classes" or functions that handle multiple unrelated tasks. **Why:** SRP simplifies code, improves testability, and reduces the risk of introducing unintended side effects when modifying existing code. **Code Example:** Adhering to Single Responsibility Principle """typescript // Good: Separate classes for user authentication and profile management // Class to Handle Authentication class AuthenticationService { async login(username: string, password: string): Promise<boolean> { // Authentication logic here console.log("Authenticating user ${username}"); return true; // Simulate successful authentication } async logout(): Promise<void> { // Logout logic here console.log('Logging out user'); } } // Class to Handle User Profiles class UserProfileService { async getUserProfile(userId: string): Promise<{ id: string; username: string; }> { // Logic to retrieve user profile console.log("Fetching profile for user ID ${userId}"); return { id: userId, username: 'exampleUser' }; // Simulate profile data } async updateUserProfile(userId: string, newData: any): Promise<void> { // Logic to update user profile console.log("Updating profile for user ID ${userId} with data:", newData); } } const authService = new AuthenticationService(); const profileService = new UserProfileService(); async function main() { const isLoggedIn = await authService.login('user123', 'password'); if (isLoggedIn) { const userProfile = await profileService.getUserProfile('user123'); console.log('User Profile:', userProfile); } } main(); """ ### 2.4 Separation of Concerns (SoC) **Standard:** Divide the application into distinct sections, each addressing a separate concern. * **Do This:** Isolate UI rendering from data fetching, business logic from infrastructure code, etc. * **Don't Do This:** Mix different concerns within the same module or component, leading to tightly coupled and difficult-to-maintain code. **Why:** SoC promotes modularity, testability, and reusability. **Code Example:** Separating data fetching concerns from UI """typescript // Bad: Mixing data fetching with UI rendering within the same component // (Leads to tight coupling and makes it difficult to test and reuse) // Consider isolating data fetching logic using custom hooks or services. import React, { useState, useEffect } from 'react'; interface User { id: number; name: string; email: string; } function UserProfileComponent({ userId }: { userId: string }) { const [user, setUser] = useState<User | null>(null); const [loading, setLoading] = useState(true); useEffect(() => { async function fetchUser() { try { const response = await fetch("https://jsonplaceholder.typicode.com/users/${userId}"); if (!response.ok) { throw new Error("HTTP error! Status: ${response.status}"); } const data: User = await response.json(); setUser(data); } catch (error) { console.error('Error fetching user:', error); } finally { setLoading(false); } } fetchUser(); }, [userId]); if (loading) { return <div>Loading user profile...</div>; } if (!user) { return <div>Failed to load user profile.</div>; } // Rendering the user profile return ( <div> <h2>User Profile</h2> <p>Name: {user.name}</p> <p>Email: {user.email}</p> </div> ); } export default UserProfileComponent; // More robust example using custom hook import React from 'react'; import { useUser } from './useUser'; // Custom hook interface User { id: number; name: string; email: string; } function UserProfileComponentHooked({ userId }: { userId: string }) { const { user, loading, error } = useUser(userId); // Use the custom hook if (loading) { return <div>Loading user profile...</div>; } if (error) { return <div>Error: {error.message}</div>; } if (!user) { return <div>User not found.</div>; } return ( <div> <h2>User Profile</h2> <p>Name: {user.name}</p> <p>Email: {user.email}</p> </div> ); } export default UserProfileComponentHooked; // Custom hook import { useState, useEffect } from 'react'; interface User { id: number; name: string; email: string; } interface UseUserResult { user: User | null; loading: boolean; error: Error | null; } export function useUser(userId: string): UseUserResult { const [user, setUser] = useState<User | null>(null); const [loading, setLoading] = useState(true); const [error, setError] = useState<Error | null>(null); useEffect(() => { async function fetchUser() { setLoading(true); setError(null); try { const response = await fetch("https://jsonplaceholder.typicode.com/users/${userId}"); if (!response.ok) { throw new Error("HTTP error! Status: ${response.status}"); } const data: User = await response.json(); setUser(data); } catch (e:any) { setError(e); } finally { setLoading(false); } } fetchUser(); }, [userId]); return { user, loading, error }; } """ ## 3. Design Patterns ### 3.1 Factory Pattern **Standard:** Use factory functions or classes to create objects, abstracting away the concrete implementation details. * **Do This:** Define a factory interface or abstract class and create concrete factories that implement the interface. * **Don't Do This:** Directly instantiate concrete classes throughout the codebase, tightly coupling code to specific implementations. **Why:** The Factory Pattern promotes loose coupling and allows for easy substitution of object implementations. **Code Example:** Factory pattern in typescript """typescript // Interface for different payment methods interface PaymentMethod { processPayment(amount: number): void; } // Concrete implementation for Credit Card payment class CreditCardPayment implements PaymentMethod { processPayment(amount: number): void { console.log("Processing credit card payment of $${amount}"); } } // Concrete implementation for PayPal payment class PayPalPayment implements PaymentMethod { processPayment(amount: number): void { console.log("Processing PayPal payment of $${amount}"); } } // Factory interface interface PaymentMethodFactory { createPaymentMethod(): PaymentMethod; } // Concrete factory for creating Credit Card payments class CreditCardPaymentFactory implements PaymentMethodFactory { createPaymentMethod(): PaymentMethod { return new CreditCardPayment(); } } // Concrete factory for creating PayPal payments class PayPalPaymentFactory implements PaymentMethodFactory { createPaymentMethod(): PaymentMethod { return new PayPalPayment(); } } // The client code that uses the factory to create payment methods class PaymentProcessor { private factory: PaymentMethodFactory; constructor(factory: PaymentMethodFactory) { this.factory = factory; } processOrder(amount: number): void { const paymentMethod = this.factory.createPaymentMethod(); paymentMethod.processPayment(amount); } } // Usage async function main() { const creditCardFactory = new CreditCardPaymentFactory(); const payPalFactory = new PayPalPaymentFactory(); const paymentProcessor1 = new PaymentProcessor(creditCardFactory); paymentProcessor1.processOrder(100); // Output: Processing credit card payment of $100 const paymentProcessor2 = new PaymentProcessor(payPalFactory); paymentProcessor2.processOrder(50); // Output: Processing PayPal payment of $50 } main(); """ ### 3.2 Observer Pattern **Standard:** Define a one-to-many dependency between objects, so that when one object changes state, all its dependents are notified and updated automatically. * **Do This:** Create a "Subject" interface that provides methods for attaching and detaching observers * **Don't Do This:** Have tight coupling between objects by directly calling methods on other objects. **Why:** The Observer Pattern decouples the subject from its observers, making it easier to add or remove observers without modifying the subject. **Code Example:** Implementation """typescript // Observer Interface interface Observer { update(message: string): void; } // Subject Interface interface Subject { attach(observer: Observer): void; detach(observer: Observer): void; notify(message: string): void; } // Concrete Observer class ConcreteObserver implements Observer { private id: number; constructor(id: number) { this.id = id; } update(message: string): void { console.log("Observer ${this.id}: Received message - ${message}"); } } // Concrete Subject class ConcreteSubject implements Subject { private observers: Observer[] = []; attach(observer: Observer): void { this.observers.push(observer); } detach(observer: Observer): void { this.observers = this.observers.filter(obs => obs !== observer); } notify(message: string): void { this.observers.forEach(observer => observer.update(message)); } // Method to update state and notify observers someBusinessLogic(): void { console.log('Subject: Doing something important.'); this.notify('Important message from Subject!'); } } // Usage async function main() { const subject = new ConcreteSubject(); const observer1 = new ConcreteObserver(1); const observer2 = new ConcreteObserver(2); const observer3 = new ConcreteObserver(3); subject.attach(observer1); subject.attach(observer2); subject.someBusinessLogic(); subject.detach(observer2); // Detach observer2 subject.attach(observer3); subject.someBusinessLogic(); } main(); """ ### 3.3 Strategy Pattern **Standard:** Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it. * **Do This:** Create a strategy interface that defines a method the strategies must implement, then each concrete strategy implements this interface. * **Don't Do This:** Hardcode the execution path. **Why:** To encapsulate variation. **Code Example:** Implementation """typescript // Strategy Interface interface SortStrategy { sort(data: number[]): number[]; } // Concrete Strategy 1: Bubble Sort class BubbleSortStrategy implements SortStrategy { sort(data: number[]): number[] { console.log('Sorting using bubble sort'); // Bubble Sort implementation const n = data.length; for (let i = 0; i < n - 1; i++) { for (let j = 0; j < n - i - 1; j++) { if (data[j] > data[j + 1]) { // Swap data[j] and data[j+1] const temp = data[j]; data[j] = data[j + 1]; data[j + 1] = temp; } } } return data; } } // Concrete Strategy 2: Quick Sort class QuickSortStrategy implements SortStrategy { sort(data: number[]): number[] { console.log('Sorting using quick sort'); // Quick Sort implementation if (data.length <= 1) { return data; } const pivot = data[0]; const left = []; const right = []; for (let i = 1; i < data.length; i++) { if (data[i] < pivot) { left.push(data[i]); } else { right.push(data[i]); } } return this.sort(left).concat(pivot, this.sort(right)); } } // Context class Sorter { private strategy: SortStrategy; constructor(strategy: SortStrategy) { this.strategy = strategy; } setStrategy(strategy: SortStrategy): void { this.strategy = strategy; } sort(data: number[]): number[] { return this.strategy.sort(data); } } // Usage async function main() { const data = [5, 2, 8, 1, 9, 4]; const bubbleSort = new BubbleSortStrategy(); const quickSort = new QuickSortStrategy(); const sorter = new Sorter(bubbleSort); // Initial strategy is Bubble Sort console.log('Sorted array using Bubble Sort:', sorter.sort([...data])); sorter.setStrategy(quickSort); // Change the strategy to Quick Sort console.log('Sorted array using Quick Sort:', sorter.sort([...data])); } main(); """ ## 4. TypeScript Specific Considerations ### 4.1 Strict Mode **Standard:** Enable TypeScript's strict mode ("strict: true" in "tsconfig.json"). * **Do This:** Embrace strict null checks, no implicit "any", and other strictness flags. Fix related typing issues. * **Don't Do This:** Disable strict mode to avoid compiler errors, as this can hide potential runtime bugs. **Why:** Strict mode enforces stricter type checking, leading to more robust and maintainable code. ### 4.2 Utility Types **Standard:** Leverage TypeScript's utility types (e.g., "Partial", "Readonly", "Pick", "Omit") to manipulate types and improve code clarity. """typescript interface User { id: string; name: string; email: string; createdAt: Date; } // Make all properties optional type PartialUser = Partial<User>; // Make all properties readonly type ReadonlyUser = Readonly<User>; // Pick only id and name properties type UserName = Pick<User, 'id' | 'name'>; // Omit the createdAt property type UserWithoutCreatedAt = Omit<User, 'createdAt'>; """ ### 4.3 Type Inference **Standard:** Take advantage of TypeScript's type inference capabilities to reduce boilerplate and improve code readability. **Code Example:** """typescript // TypeScript infers the type of 'message' to be string const message = "Hello, TypeScript!"; // TypeScript infers the return type of the function function add(a: number, b: number) { return a + b; } """ ### 4.4 Declaration Files **Standard:** Provide declaration files (".d.ts") for libraries or modules to enable type checking and code completion for consumers. * **Do This:** Use automatic declaration generation ("declaration: true" in "tsconfig.json") or manually create declaration files when necessary. * **Don't Do This:** Ship JavaScript code without corresponding declaration files, limiting the usability of the code in TypeScript projects. ### 4.5 Advanced Types **Standard:** Use advanced TypeScript features like discriminated unions, conditional types, and mapped types where appropriate to model complex data structures and relationships. """typescript // Discriminated Union interface Circle { kind: 'circle'; radius: number; } interface Square { kind: 'square'; sideLength: number; } type Shape = Circle | Square; function getArea(shape: Shape): number { switch (shape.kind) { case 'circle': return Math.PI * shape.radius ** 2; case 'square': return shape.sideLength ** 2; } } """ ### 4.6 Decorators **Standard:** Use decorators to add metadata or modify the behavior of classes, methods, or properties, but adhere to a consistent style, avoid complex implementations, and be aware of potential performance implications. """typescript function LogClass(constructor: Function) { console.log("Class ${constructor.name} is being decorated."); } @LogClass class MyClass { constructor() { console.log('MyClass constructor called.'); } } function LogMethod(target: any, propertyKey: string, descriptor: PropertyDescriptor) { const originalMethod = descriptor.value; descriptor.value = function(...args: any[]) { console.log("Method ${propertyKey} is being called with arguments:", args); const result = originalMethod.apply(this, args); console.log("Method ${propertyKey} returned:", result); return result; }; return descriptor; } class Calculator { @LogMethod add(a: number, b: number): number { return a + b; } } """ ### 4.7 Use "unknown" type where appropriate **Standard:** Use "unknown" instead of "any" when you need to represent a value of any type but want to ensure type safety. "unknown" forces you to perform type narrowing before using the value, providing better type safety than casually using "any", while not necessarily knowing the implementation types at compile time. """typescript function processData(data: unknown): void { if (typeof data === 'string') { console.log(data.toUpperCase()); // OK, data is string here } else if (typeof data === 'number') { console.log(data * 2); // OK, data is number here } else { console.log('Data is of unknown type'); } } """ These core architecture standards provide a comprehensive foundation for building robust, scalable, and maintainable TypeScript applications. By adhering to these guidelines, development teams can improve code quality, reduce technical debt, and accelerate development.