How to Use @Module Decorator in NestJS: Simple Guide

In NestJS, use the @Module decorator to define a module that groups related controllers, providers, and imports. It organizes your app into cohesive blocks by specifying imports, controllers, providers, and exports inside the decorator.

Syntax

The @Module decorator takes an object with these main properties:

• imports: Other modules to include.
• controllers: Controllers to handle incoming requests.
• providers: Services or providers to inject.
• exports: Providers to share with other modules.

typescript

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

@Module({
  imports: [],
  controllers: [],
  providers: [],
  exports: [],
})
export class YourModule {}

Example

This example shows a simple module with one controller and one service. The @Module decorator groups them together so NestJS knows how to build the app.

typescript

import { Module } from '@nestjs/common';
import { CatsController } from './cats.controller';
import { CatsService } from './cats.service';

@Module({
  controllers: [CatsController],
  providers: [CatsService],
})
export class CatsModule {}

Output

No direct output; NestJS uses this module to organize app components.

Common Pitfalls

Common mistakes include:

• Forgetting to add controllers or providers inside the @Module decorator, so NestJS can't find them.
• Not importing dependent modules in imports, causing injection errors.
• Trying to use providers without exporting them if they are needed in other modules.

typescript

/* Wrong: Missing provider in module */
import { Module } from '@nestjs/common';
import { CatsController } from './cats.controller';

@Module({
  controllers: [CatsController],
  // providers: [CatsService], // Forgot this line
})
export class CatsModule {}

/* Right: Include provider */
import { Module } from '@nestjs/common';
import { CatsController } from './cats.controller';
import { CatsService } from './cats.service';

@Module({
  controllers: [CatsController],
  providers: [CatsService],
})
export class CatsModule {}

Quick Reference

Use this quick guide to remember the @Module decorator parts:

Property	Purpose
imports	List other modules to include
controllers	List controllers handling requests
providers	List services or providers to inject
exports	List providers to share with other modules

Key Takeaways

Use @Module to group related controllers and providers in NestJS.

Always list controllers and providers inside the @Module decorator.

Import dependent modules in the imports array to use their exports.

Export providers if other modules need to use them.

Missing providers or imports causes injection errors.