Application lifecycle in NestJS - Mini Project: Build & Apply

Understanding Application Lifecycle in NestJS

📖 Scenario: You are building a simple NestJS service that logs messages during different stages of the application lifecycle. This helps you understand how NestJS manages startup and shutdown events.

🎯 Goal: Create a NestJS service that uses lifecycle hooks to log messages when the application starts and stops.

📋 What You'll Learn

Create a service class named AppLifecycleService

Implement the OnModuleInit interface and its onModuleInit() method

Implement the OnModuleDestroy interface and its onModuleDestroy() method

Log 'Application has started' inside onModuleInit()

Log 'Application is shutting down' inside onModuleDestroy()

💡 Why This Matters

🌍 Real World

Understanding application lifecycle hooks helps developers run setup and cleanup code automatically in NestJS applications, such as connecting to databases or closing resources.

💼 Career

Many backend developer roles require knowledge of framework lifecycle events to manage resources efficiently and ensure smooth application startup and shutdown.

1

Create the service class

Create a class called AppLifecycleService and export it.

NestJS

# Create and export a class named AppLifecycleService
# Your code here

Need a hint?

Use export class AppLifecycleService {} to create the class.

2

Add lifecycle interfaces

Import OnModuleInit and OnModuleDestroy from @nestjs/common. Then make AppLifecycleService implement both interfaces.

NestJS

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

export class AppLifecycleService implements OnModuleInit, OnModuleDestroy {
  # Your code here
}

Need a hint?

Use implements OnModuleInit, OnModuleDestroy after the class name.

3

Add lifecycle methods with logs

Inside AppLifecycleService, add the method onModuleInit() that logs 'Application has started'. Also add onModuleDestroy() that logs 'Application is shutting down'. Use console.log() for logging.

NestJS

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

export class AppLifecycleService implements OnModuleInit, OnModuleDestroy {
  // Add onModuleInit() and onModuleDestroy() methods with console.log
  # Your code here
}

Need a hint?

Define both methods exactly as named and use console.log with the exact messages.

4

Export the service for use

Ensure the AppLifecycleService class is exported so it can be used in other parts of the application.

NestJS

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

// Confirm the class is exported
# Your code here

Need a hint?

Make sure the export keyword is before the class declaration.