Service creation in NestJS - Performance & Optimization

Performance: Service creation

MEDIUM IMPACT

Service creation affects initial application startup time and memory usage, impacting how fast the app becomes responsive.

Creating services eagerly at app startup

NestJS

import { Injectable, OnModuleInit } from '@nestjs/common';

@Injectable()
export class HeavyService implements OnModuleInit {
  private initialized = false;

  async onModuleInit() {
    // defer heavy logic asynchronously
    await this.lazyInit();
  }

  private async lazyInit() {
    if (!this.initialized) {
      // heavy initialization logic
      this.initialized = true;
    }
  }
}

// In AppModule providers: [HeavyService]

Defers heavy initialization asynchronously after startup, improving responsiveness.

📈 Performance Gainreduces startup blocking time by 80-90%

Creating services eagerly at app startup

NestJS

import { Injectable } from '@nestjs/common';

@Injectable()
export class HeavyService {
  constructor() {
    // heavy initialization logic
  }
}

// In AppModule providers: [HeavyService]

Service initializes heavy resources immediately, delaying app startup.

📉 Performance Costblocks app startup for 100+ ms depending on logic

Performance Comparison

Pattern	Startup Delay	Memory Usage	Responsiveness	Verdict
Eager heavy service creation	High (100+ ms)	High	Slow initial response	[X] Bad
Lazy asynchronous service init	Low (10-20 ms)	Moderate	Fast initial response	[OK] Good

Rendering Pipeline

Service creation happens during app bootstrap before rendering. Heavy synchronous service initialization delays the app becoming interactive.

→App Initialization

→Module Loading

⚠️ BottleneckSynchronous heavy logic in service constructors or lifecycle hooks

Optimization Tips

1Avoid heavy synchronous logic in service constructors.

2Use async lifecycle hooks for deferred initialization.

3Lazy load services if possible to reduce startup delay.

Performance Quiz - 3 Questions

What is the main performance risk of creating heavy services eagerly in NestJS?

A It blocks app startup and delays responsiveness

B It increases network requests

C It causes layout shifts in the browser

D It reduces CSS selector efficiency

DevTools: Performance

How to check: Record a startup profile in DevTools or Node.js profiler, look for long blocking tasks during app bootstrap.

What to look for: Long synchronous tasks in service constructors or OnModuleInit hooks indicate blocking service creation.