Dynamic modules in NestJS - Mini Project: Build & Apply

Creating a Dynamic Module in NestJS

📖 Scenario: You are building a NestJS application that needs a configurable logging module. This module should allow different parts of the app to use it with custom settings.

🎯 Goal: Create a dynamic module called LoggerModule that accepts a configuration object with a logLevel property. This module should provide a LoggerService that uses the configured logLevel.

📋 What You'll Learn

Create a LoggerModule class with a static forRoot method that accepts a config object with logLevel string property.

Inside forRoot, return a dynamic module with module, providers, and exports properties.

Create a LoggerService class that uses the injected logLevel to control logging.

Use NestJS dependency injection to provide the logLevel value to LoggerService.

💡 Why This Matters

🌍 Real World

Dynamic modules let you build reusable NestJS modules that can be configured differently in various parts of your app, like database connections or logging.

💼 Career

Understanding dynamic modules is essential for building scalable and maintainable NestJS applications in professional backend development.

1

Create the LoggerModule class with forRoot method

Create a class called LoggerModule with a static method forRoot that accepts a parameter options of type { logLevel: string }. The method should return an object with a module property set to LoggerModule.

NestJS

class LoggerModule {
  // Your code here
}

Need a hint?

Define a class and a static method that returns an object with a module property.

2

Add provider for logLevel token

Inside the forRoot method of LoggerModule, add a providers array to the returned object. This array should contain an object with provide set to 'LOG_LEVEL' and useValue set to options.logLevel. Also add exports array with 'LOG_LEVEL'.

NestJS

class LoggerModule {
  static forRoot(options: { logLevel: string }) {
    return {
      module: LoggerModule,
      // Your code here
    };
  }
}

Need a hint?

Add providers and exports arrays to the returned object in forRoot.

3

Create LoggerService using injected logLevel

Create a class called LoggerService with a constructor that injects logLevel using @Inject('LOG_LEVEL'). Store it in a private readonly property called logLevel. Add a method log that accepts a message string and logs it only if logLevel is not 'none'.

NestJS

class LoggerModule {
  static forRoot(options: { logLevel: string }) {
    return {
      module: LoggerModule,
      providers: [
        {
          provide: 'LOG_LEVEL',
          useValue: options.logLevel
        }
      ],
      exports: ['LOG_LEVEL']
    };
  }
}

// Your code here

Need a hint?

Use @Inject('LOG_LEVEL') in the constructor to get the log level value.

4

Add LoggerService provider and export to LoggerModule

In the forRoot method of LoggerModule, add LoggerService to the providers array and also add it to the exports array.

NestJS

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

class LoggerModule {
  static forRoot(options: { logLevel: string }) {
    return {
      module: LoggerModule,
      providers: [
        {
          provide: 'LOG_LEVEL',
          useValue: options.logLevel
        },
        // Add LoggerService provider here
      ],
      exports: ['LOG_LEVEL' /* Add LoggerService export here */]
    };
  }
}

class LoggerService {
  constructor(@Inject('LOG_LEVEL') private readonly logLevel: string) {}

  log(message: string) {
    if (this.logLevel !== 'none') {
      console.log(`[${this.logLevel}] ${message}`);
    }
  }
}

Need a hint?

Add LoggerService to both providers and exports arrays in forRoot.