[Nest.js] 14 - Log basic

Contents
1. Log?
2. Types of Logging
3. Log Level Example
4. logging Implementation

---

1. Log?

- When we run an application, we encount unexpected errors sometimes.

- Therefore, to see logs is a fast and useful way to find where an error occurs.

- It is a better way to put logs after every single implementation is done

- Nest.js provides Logger class, which is built-in.

---

2. Types Of Logging

- Log : A wide use of logging for an important infornmation

- Warning : unhandled issue which is NOT fatal or destructive

- Error : unhandled issue which is fatal or destructive

- Debug : when an error occurred, Debug logging is helpful to degub a login, intended for developers

- Verbose :  provides an insight of information about application running, intended for operators

---

3. Log Level Example

	LOG	Error	Warning	Debug	Verbose
Development	O	O	O	O	O
Staging	O	O	O	X	X
Productuib	O	O	X	X	X

// this is one of logging level cases, so it might be different based on application environment.

---

4. logging Implementation

- src/main.ts

import { Logger, ValidationPipe } from '@nestjs/common';
...

async function bootstrap() {
  const logger = new Logger();// 1
  const app = await NestFactory.create(AppModule);

  ...

  const port = 3000;
  await app.listen(port);
  
  logger.log(`Application running on port ${port}`); // 2
  Logger.log(`Application running on port ${port}`); // 3
}
bootstrap();

// 1. create an instance of Logger class, which is nest.js built-in

// 2. use the method log(...), already implemented in its class

// 3. use the static method log(...), already implemented in its class,

- Check logs 

 

 

- src/boards/boards.controller.ts

...
import {
  ...
  Logger,
} from '@nestjs/common';

@Controller('boards')
@UseGuards(AuthGuard())
export class BoardsController {
  private logger = new Logger('JamesBoardsController'); // 1

  constructor(private boardsService: BoardsService) {}

  ...

  @Get()
  getAllBoards(@GetUser() user: User): Promise<Board[]> {
    this.logger.log(`User ${user.username} trying to get all boards`); // 2
    this.logger.error(`User ${user.username} trying to get all boards`); // 3
    this.logger.warn(`User ${user.username} trying to get all boards`); // 4
    this.logger.debug(`User ${user.username} trying to get all boards`); // 5
    this.logger.verbose(`User ${user.username} trying to get all boards`); // 6
    return this.boardsService.getAllBoards(user);
  }

  @Post()
  createBoard(
    @Body() createBoardDto: CreateBoardDto,
    @GetUser() user: User,
  ): Promise<Board> {
    this.logger.verbose(
      `User ${user.username} creating a new board. 
      Payload : ${JSON.stringify(createBoardDto)}`, // 7
    );
    return this.boardsService.createBoard(createBoardDto, user);
  }

  ...
}

// 1. new Logger('JamesBoardsController')  - label of the Logger class

// 2 ~ 6. see what differences are between those methods

// 7 ${ JSON.stringify(createBoardDto) - to make an object to JSON format

 

- Sign in  the user "jamescha"

 

- Console logs for Read all boards with his token

// Green - logger.log
// Red - logger.error
// Yellow - logger.warn
// Purple - logger.debug
// Blue - logger.verbose