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npm i -S yup @bluelibs/logger-bundle
import { LoggerBundle } from "@bluelibs/logger-bundle";
const kernel = new Kernel({  bundles: [new LoggerBundle()],});


This bundle allows you to log information that happens in your sistem. The logger can optionally output to console.log but later on, as your system grows, all of your instances should output to a centralised log management place. This is why we strongly recommend, as you're building your app, to use LoggerService instead of console.log, it will pay off.

If you want to use it:

const logger = container.get(LoggerService);"User access forbidden");
// Add more context to your"User access forbidden", { route: "/123" }); // You can do anything you like to your context
// Some other type of logslogger.warning("User access forbidden");logger.error("User access forbidden");logger.critical("User access forbidden");

The log object created looks like this:

export interface ILog {  message: string;  level: LogLevel; // INFO, ERROR, WARNING, CRITICAL  context: any;}

If you want to listen to event and email all the critical ones:

import { Listener, On } from "@bluelibs/core";import { LogEvent, LogLevel } from "@bluelibs/logger-bundle";
export class EmailCriticalLogs extends Listener {  constructor(protected readonly emailService: EmailService) {}
  @On(LogEvent)  onLog(e: LogEvent) {    const log =;
    if (log.level === LogLevel.CRITICAL) {      // this.emailService.send()    }  }}

And ofcourse don't forget to register you listener:

class AppBundle extends Bundle {  async prepare() {    // Warming up simply means instantiating and running init so it attaches events    this.warmup([EmailCriticalLogs]);  }}

Custom Log Object

You can customise your Log model if you want for example specific contexts or other stuff:

import { LoggerService, Log, LogLevel } from "@bluelibs/logger-bundle";
class UserLog extends Log<{ userId: string }> {}
const logger = container.get(LoggerService);
// This will get dispatched, and next you can do custom compute for your log by checking instance oflogger.send(new UserLog("message", LogLevel.INFO, { userId: "XXX" }));

You can identify in your log listeners where this is a UserLog via instanceof.



It's just logging, simple and scalable.



  • Use the 4 types of log levels and send out some messages (1p)
  • Listen to events that are of custom type, like UserLog and perform an operation on it (2p)