Node.js logger overview – step-by-step information, instruments, greatest practices

When completed badly, logging in Node.js is little greater than a nuisance that provides to the variety of issues a (bored) developer must care about. When completed appropriately, it may be an important and extremely helpful component at each stage of improvement – from coding to debugging, to planning for brand spanking new options. Let’s embrace the advantages of logging by studying about the most effective Node.js loggers and greatest practices for his or her use.

On this article, I’m going to provide you a stable introduction to Node.js loggers. I’m going to go over:

  • definitions and different vital terminology that has to do with Node.js logging.
  • the configuration required to arrange a logging software.
  • greatest practices of utilizing Node.js loggers.
  • the elements that (will) affect your choice about which logger instrument to make use of. 

Let’s get proper to it!

Who makes use of Node.js loggers?

Node.js loggers have at all times appeared to be a considerably underappreciated component of improvement to me.

Actually, many builders I do know by no means even received to arrange a Node.js logger on their very own since, by the point they be a part of a brand new undertaking, the logger is already put in place by another person.

However when you concentrate on it, loggers actually do matter for all actors in a software program improvement undertaking.

Builders and DevOps engineers

They use loggers to debug code. The logging entries will alert them of bizarre occurrences within the app comparable to inadequate reminiscence or failure to retrieve a particular piece of information.

Technical entrepreneurs 

They will use the logging information to trace the efficiency of their software program. Significantly expert ones may even create their very own customized campaigns, log occasions, and ship the info over to a third-party instrument for additional processing and evaluation.

Knowledge scientists 

They will arrange and optimize loggers to file simply the info they want in a format appropriate for them. They go on to interpret the info as a way to make knowledgeable selections about merchandise, companies, and even the entire world round them. For instance, they will discover patterns for joint buying of particular merchandise in each bodily shops (e.g. massive chain supermarkets) and digital shops. Such merchandise can then be saved collectively or provided in a bundle to extend gross sales. Such purposes of loggers verge on information mining or machine studying. They’re in nice demand among the many greatest gamers in industries comparable to commerce, manufacturing, geophysics, and plenty of extra.

However it all might sound slightly bit summary whenever you don’t have precise sensible expertise in utilizing logging purposes.

Let’s get some apply, then!

Node.js logging – fundamentals

As I’ve already stated, many builders, not to mention different staff members in a undertaking, don’t suppose twice about logging.

What’s logging all about?

Logging is the act of recording an occasion incidence, information circulate, or manipulation in laptop software program. It helps you perceive how the software program really runs. It makes it a lot simpler to debug and enhance your code when it misbehaves.

There are various approaches to logging. The three most common ones embody:

  • Merely printing out to a console or customary output (stdout).
  • Using libraries that make printing extra uniform and structured.
  • Utilizing specialised software program that captures, shops, and permits evaluation of saved information.

On this article, I’m referencing Node.js libraries and utilities. Nevertheless, a lot of the concepts aren’t Node.js-specific and will be prolonged or utilized to different programming languages or environments.

Software logging challenges

There are some challenges to software logging that you just, as an aspiring information wizard, need to resolve:

  • What format ought to I write my messages in (easy string, JSON, or another structured format)?
  • The place do I need to ship and retailer my messages (stdout, filesystem, database, or an exterior instrument comparable to ELK stack)?
  • If I resolve on storing in a filesystem, do I need to put logs in a single file or a number of ones?
  • How do I identify these log recordsdata? What standards ought to I apply when deciding on which file I need to write to?
  • How lengthy do I need to retailer my logs?
  • Which of the various log administration instruments or libraries do I select for logging? Do I even want one within the first place?
  • What data ought to I log and which I have to not?
  • What number of logs is sufficient?

Sadly, I received’t provide you with a particular reply to any of them as a result of solutions are particular to every use case. However don’t go away – I’ll give you common pointers on the right way to strategy these challenges.

Node.js logger – the case for logging libraries

Whereas it’s definitely attainable to simply print to a stdout utilizing a built-in toll (comparable to console.log in JavaScript), making significant and helpful log messages that means can be tedious and easily not possible, as it will power you to spend an excessive amount of time on repetitive duties, having to sort the instructions manually. Logging libraries are there that will help you with that (and way more).

Listed below are among the hottest Node.js logging libraries by the variety of GitHub stars.


One of the vital widespread logging library instruments. That is my typical logger of selection. It’s compact and gives the whole lot you may want from a logger, together with ranges (sorting messages by significance), formatting (regarding construction and syntax of log entries), totally different transports (storage for logs), and so forth. It’s also extremely configurable.


This one gives very related performance to Winston. It boasts little or no overhead and supplies transports in addition to log processing. It additionally gives a pretty-pino module for formating logs throughout improvement utilizing NDJSON (Newline Delimited JSON).


It’s a easy and quick JSON logging library. It comes with a CLI instrument for shopping and pretty-printing logs. It gives customized log rendering with serializers, and logger specialization with log.youngster. As well as, it streams for specifying log targets. 

Methods to configure a Node.js logger?

In fact, as is often the case in our discipline of labor, configuration necessities for Node.js loggers depend upon many elements, together with what you really need to log. I’m going to give you some choices on the right way to configure your logger, however in the end it’s as much as you what you select to or to not embody in your subsequent undertaking. Nevertheless, this instance configuration ought to provide you with an thought of the right way to go about it.

This can be a configuration instance based mostly on our open-source module. Let’s break it down.

Beneath you may see the overview of a Winston logger configuration that The Software program Home staff used on this undertaking. The feedback you could see within the code describe how and why ranges, codecs, and transports for our log entries are arrange.

How precisely will your log entries look? The code beneath exhibits the exact log format that takes into consideration information masking (i.e. obfuscation) for delicate information.

This information masking performance itself wants some configuration. Right here’s the way it’s achieved on this undertaking.

And right here is an instance log that incorporates masked information. Discover the way in which sure parts are obfuscated within the end result code.

This can be a easy instance, but it surely does cowl all the fundamentals:

  • Categorization of your logs.
  • The best way your logs look.
  • The strategy for storing your logs.
  • Guidelines of information masking that defend delicate information (vital in loads of industrial tasks).

There’s much more to be discovered about logs earlier than you need to use them safely and effectively. Enter greatest practices.

The Software program Home’s Node.js boilerplate helps you arrange your undertaking shortly. It helps superior logging by way of the Winston library. Test it out!

Finest practices of utilizing Node.js loggers

No matter how a lot you already know about organising Node.js logger from a technical standpoint, you received’t get a lot worth from logging in the event you don’t stick with some greatest practices. For starters…

You’ve received to know what to log:

  • Attempt to cowl vital flows of your app and determine what data shall be useful in debugging a difficulty in manufacturing.
  • Log errors when they’re really errors (e.g. not discovering a useful resource for GET /useful resource/{id} most likely isn’t an error, however a failure to discover a person for GET /me when there’s a person token may be one). Lacking a useful resource beneath PATCH /useful resource/{id} clearly is just not an accurate scenario
  • Undoubtedly log uncaught exceptions and unhandled rejections.
  • Log information that’s helpful for app profiling (an in-depth evaluation of app efficiency, all the way down to all of its capabilities individually).

There are additionally some issues that you must undoubtedly skip when logging in a Node.js app.

What you undoubtedly NOT need to log:

  • Personally identifiable data (PII) and different delicate sorts of information ought to be averted. Examples of such information can be emails in addition to telephone, bank cards, CVC, financial institution accounts, and social safety numbers.

Use log ranges


Jokes apart, it actually is useful to categorize your logs. That means, you may type by way of them much more simply. You’ll know which logs will be safely ignored or no less than put apart quickly, and which require you to behave shortly.

Relying on the library of your selection, there are numerous strategies of logging messages in a unique method based mostly on their significance or severity. They’re usually based mostly on the Syslog Protocol. Such categorization techniques make it simple to type by way of all of the logging messages as a way to take care of them accordingly. A typical set of ranges embody:

  • ERROR – signifies an error, which must be addressed. A difficulty like this usually doesn’t stop the app from working.
  • INFO – common information. It could embody data on what sort of information was obtained by the app and when it was obtained.
  • DEBUG – debug logs are used throughout improvement and debugging and ought to be switched off in manufacturing.
  • WARN – it informs about errors that typically don’t actually warrant any motion on our aspect (e.g. incorrect information obtained from the person or third-party API).
  • FATAL – a really critical subject has arisen, which requires your rapid consideration. This subject might end in an software shutdown.

Make your logs significant and informative:

The textual content information handed in logs ought to be exact sufficient to really assist remedy a difficulty. You may suppose that it isn’t such an enormous deal when the messages are few. However the larger the system, the extra of a distinction good naming practices matter.

Examples of excellent logs:

  • File xyz.pdf not discovered.
  • Consumer {id} not discovered.
  • Failed transitioning of transaction abc: can not transition abc from the pending to lively state.

Instance of poor logs:

  • File not discovered.
  • Flawed state.

I want to suggest a simple rule of thumb for naming logs:

 If there isn’t any placeholder for significant information comparable to ID, enum worth, or file identify, the log is probably sub-par.

In fact, some commonsense changes apply to this rule. If you’re in some form of logical department in your code and there’s no technique to confuse or misread your values, you may hardcode them. For instance, in the event you configure part of your system fully devoted to the method of account activation, you may get away with logging logger.information(“Can’t activate account”) as an alternative of logger.information(“Can’t set standing to %s”, standing).

Prolong performance & usability utilizing loggers

Some widespread logger libraries include functionalities that stretch the performance or usability of a typical logging regime. It’s value it to provide them a strive. For instance:

  • logger.youngster(choices) – creates a specialised logger object that provides a handed choices object with every subsequent log, enabling increased contextualization.
  • Log message interpolation splat comparable to logger.information(”Acquired message %o“, message):
    • %o – permits stringifying handed object,
    • %s – fills a string in,
    • %d – passes in a quantity.

Right here is the kid logger initialization. It contains an instance of log outputs for default and youngster loggers.

Standardize guidelines for logging in your software

Set up some guidelines for logging in your software. Every system is totally different so these directives will differ from codebase to codebase. When designing your personal, mix undertaking necessities with common suggestions. An excellent instance of the latter can be OWASP pointers.

Are you recent with all the newest Node.js options? Try our Node.js options overview to brush up

How to decide on a Node.js logger?

With a purpose to reply this query, I’ll recall the decision-making course of that I utilized in a latest undertaking of mine. My teammates and I contemplated the very same query – which logging library to decide on. There’s an abundance of them and plenty of many really feel very related.

I began by reviewing the preferred ones, comparable to Winston, Pino, Bunyan, or npmlog. I used to be their weekly downloads, stars on Github, the variety of points reported, and the final model revealed. None of these elements by themselves inform you if the library is sweet or dangerous. However collectively, they will current an image of the library’s setting, particularly whenever you perceive the context of your findings.

To offer you an instance, the library with probably the most weekly downloads was npmlog, having received almost 3 times the variety of downloads of the runner-up. Nevertheless, this worth is inflated resulting from npm being the inner logging library of npm. As such, it’s linked to many widespread libraries. It additionally felt sub-par when it comes to performance.

Alternatively, I heard good issues from my teammates about Bunyan. That is non-quantitative data, however actual sensible expertise with a instrument is efficacious. Bunyan has good stats, but it surely felt slightly bit stale with the final revealed model relationship over a 12 months again. 

One may say: effectively, what are you able to add to a longtime logging library? Whereas this may be true, there are some safety points surfacing once in a while and it’s good having them patched as quickly as attainable, particularly in purposes that depend on safety, comparable to banking apps.

Finally, I used to be torn between Winston and Pino. Each provide the whole lot one would want. They’re additionally each widespread and supported by a really lively group. In the long run, we determined to go along with Pino.

What tipped the stability in favor of Pino was the truth that it built-in neatly with the NestJS framework that we used within the undertaking. Whereas each Winston and Pino had a library that adapts them with NestJS, Pino gave us an HTTP request logging out of the field. The configuration was pretty easy and nice, It additionally boasts very low overhead when used, which is at all times a welcome factor.

The progressive Node.js framework Nest.js is an more and more widespread instrument at The Software program Home. Try our Expertise Radar to be taught extra in regards to the applied sciences we like utilizing.

Node.js loggers – conclusions

And that’s it for the loggers’ information! Whereas it isn’t that prolonged, amazingly it nonetheless takes extra time to learn than some Node.js builders dedicate to configuring loggers of their tasks!

I’m positive you’re not certainly one of them – you’re higher than that! However simply in case you want a fast refresher:

  • Logging in a Node.js app helps you enhance your code and shortly react to undesirable conditions, together with people who trigger the app to crash.
  • Earlier than you get to precise logging, you could analyze your system and resolve on what to log and what to not log. Overlogging is simply as dangerous as beneath logging – an extra of pointless data could make it harder to course of the dear half. Apart from, there may be additionally delicate information that you shouldn’t log. On this case, information masking will assist.
  • Getting aware of greatest practices of logging and growing a project-specific listing of this type for all of your staff members to comply with is certainly the way in which to go.
  • There are loads of Node.js logger instruments and fairly a couple of of them are viable choices on your undertaking. Choose the one that you just like working with greatest!

I extremely encourage you to take a better have a look at the code and group of the open-source undertaking I linked beforehand within the configuration part. I highlighted a very powerful elements, however the entire thing ought to provide you with much more sensible insights on the right way to incorporate loggers in your undertaking.

Need much more skilled Node.js data?

Try our State of Microservices 2020 report and study microservices- and Node.js-related traits and practices as advised by +650 tech leaders.

Karol Goraus

Karol Goraus

Node.js Developer

Graduate of biotechnology turned PHP programmer turned Node.js programmer. Since he loves finding out, he at all times retains on studying new applied sciences & greatest practices. Self-proclaimed bookworm (fan of S.King, H.P.Lovecraft, Tolkien, or F.Herbert). When the climate is dangerous, he performs MMORPG and strategic video games or watches anime/manga. If it’s good, he does sports activities, particularly impediment course working!


Leave a Reply

    Your Cart
    Your cart is emptyReturn to Shop