861b28b965
New skills (14): - nestjs-best-practices: 40 priority-ranked rules (kadajett) - fastapi: Pydantic v2, async SQLAlchemy, JWT auth (jezweb) - architecture-patterns: Clean Architecture, Hexagonal, DDD (wshobson) - python-performance-optimization: Profiling and optimization (wshobson) - ai-sdk: Vercel AI SDK streaming and agent patterns (vercel) - create-agent: Modular agent architecture with OpenRouter (openrouterteam) - proactive-agent: WAL Protocol, compaction recovery, self-improvement (halthelobster) - brand-guidelines: Brand identity enforcement (anthropics) - ui-animation: Motion design with accessibility (mblode) - marketing-ideas: 139 ideas across 14 categories (coreyhaines31) - pricing-strategy: SaaS pricing and tier design (coreyhaines31) - programmatic-seo: SEO at scale with playbooks (coreyhaines31) - competitor-alternatives: Comparison page architecture (coreyhaines31) - referral-program: Referral and affiliate programs (coreyhaines31) README reorganized by domain: Code Quality, Frontend, Backend, Auth, AI/Agent Building, Marketing, Design, Meta. Mosaic Stack is not limited to coding — the Orchestrator serves coding, business, design, marketing, writing, logistics, and analysis. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
110 lines
2.8 KiB
Markdown
110 lines
2.8 KiB
Markdown
---
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title: Use Async Lifecycle Hooks Correctly
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impact: HIGH
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impactDescription: Improper async handling blocks application startup
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tags: performance, lifecycle, async, hooks
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---
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## Use Async Lifecycle Hooks Correctly
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NestJS lifecycle hooks (`onModuleInit`, `onApplicationBootstrap`, etc.) support async operations. However, misusing them can block application startup or cause race conditions. Understand the lifecycle order and use hooks appropriately.
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**Incorrect (fire-and-forget async without await):**
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```typescript
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// Fire-and-forget async without await
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@Injectable()
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export class DatabaseService implements OnModuleInit {
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onModuleInit() {
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// This runs but doesn't block - app starts before DB is ready!
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this.connect();
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}
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private async connect() {
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await this.pool.connect();
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console.log('Database connected');
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}
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}
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// Heavy blocking operations in constructor
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@Injectable()
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export class ConfigService {
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private config: Config;
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constructor() {
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// BLOCKS entire module instantiation synchronously
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this.config = fs.readFileSync('config.json');
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}
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}
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```
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**Correct (return promises from async hooks):**
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```typescript
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// Return promise from async hooks
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@Injectable()
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export class DatabaseService implements OnModuleInit {
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private pool: Pool;
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async onModuleInit(): Promise<void> {
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// NestJS waits for this to complete before continuing
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await this.pool.connect();
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console.log('Database connected');
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}
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async onModuleDestroy(): Promise<void> {
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// Clean up resources on shutdown
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await this.pool.end();
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console.log('Database disconnected');
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}
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}
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// Use onApplicationBootstrap for cross-module dependencies
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@Injectable()
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export class CacheWarmerService implements OnApplicationBootstrap {
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constructor(
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private cache: CacheService,
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private products: ProductsService,
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) {}
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async onApplicationBootstrap(): Promise<void> {
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// All modules are initialized, safe to warm cache
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const products = await this.products.findPopular();
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await this.cache.warmup(products);
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}
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}
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// Heavy init in async hooks, not constructor
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@Injectable()
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export class ConfigService implements OnModuleInit {
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private config: Config;
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constructor() {
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// Keep constructor synchronous and fast
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}
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async onModuleInit(): Promise<void> {
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// Async loading in lifecycle hook
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this.config = await this.loadConfig();
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}
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private async loadConfig(): Promise<Config> {
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const file = await fs.promises.readFile('config.json');
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return JSON.parse(file.toString());
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}
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get<T>(key: string): T {
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return this.config[key];
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}
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}
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// Enable shutdown hooks in main.ts
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async function bootstrap() {
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const app = await NestFactory.create(AppModule);
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app.enableShutdownHooks(); // Enable SIGTERM/SIGINT handling
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await app.listen(3000);
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}
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```
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Reference: [NestJS Lifecycle Events](https://docs.nestjs.com/fundamentals/lifecycle-events)
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