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Daniel Golant
Daniel Golant

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What JS Logging library / tool do you use?

#discuss #javascript #node #logging

I am trying to decide on what logging module to try out for my next project. I'd love the dev community's input on:

A) What logging lib you use
B) Whether you structure your logs (and how)
C) Where you store your logs or any other logging infra you have

I have been using Winston, but I would like something that supports structured logging out of the box. The general ecosystem on NPM seems to be pretty split, and some options seem to be popular but un-maintained.

Top comments (44)

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tux0r profile image
tux0r • • Edited

There is only one thing I use:

console.log()

And I reset (and remove) my logs after the code has been proven stable. :-) Generally, logging should remain a debugging feature. The users won't need it.

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Stijn de Witt •

The problem with using console directly is that there are browsers out there (probably only real old ones though) that simply crash your code right away because console is undefined when the developer tool is not opened. Also some interpreters, such as Nashorn which comes with Java, simply do not have a console defined.

If you want to avert that risk and still only use the console for logging, you should write code similar to this:

var log = (typeof console != 'undefined') && console 
// Testing with typeof is better than window.console 
// since it works everywhere, inclucing Node JS / Nashorn
log && log.info('If the console is not there, this code will not crash')

However, this means testing log before each call to log.info... You could maybe do this to prevent that test:

var log = typeof console != 'undefined' ? console : {info:function(){}}
log.info('This code calls a dummy function if console is not there')

However, you would also have to make dummies for warn(), error() etc... In the end you would be building a shim... Which is exactly how ulog started. I understand your desire to keep logging simple and not use any external libs for it... But really the state of JS today is that 'simple' logging either is broken (crashes on some systems), is not actually 'simple' (see code examples above), or does use a library. I built ulog from the desire to make it as close to using no lib at all, while actually solving those problems. If you never use any logging lib, ulog was built with you in mind! Please try it and let me know.

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ben profile image
Ben Halpern •

I also do this. But I’m curious about other answers in the thread.

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Leonardo Teteo •

Since I'm just starting learning node I came to this post with some hesitation since I really didn't know if console.log() was an acceptable answer. Thanks for the clarification. hahaha

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Stijn de Witt •

Before I proceed I must warn you I am the author of the logging library I am using, so there is a tiny possibility that I might be biased. Very tiny :)

ulog - The microscopically small universal logger

Basically ulog is debug meets loglevel meets the console. It works in Node JS and all major browsers (even old ones!)

  • Mostly works exactly like the console does
  • Supports levels that map to console methods (info, warn, error...)
  • Supports configuration of log level via query string/localStorage (browser) or environment variables (Node)
  • Supports a debug mode that selectively enables loggers
  • Smart default log levels

Why I built it

It started out because using console directly is basically VERBOTEN. Because some browsers simply don't support it and will crash your code. Also you need to remove these statements afterwards etc. Making logging difficult and error prone. So it started as a tiny shim that just makes sure that your code never crashes or fails whether console is available or not.

I then decided I wanted log level support so I added that. And then I discovered debug, which is GREAT, and I decided to copy those features I loved about that.

Why I think it is one of the best loggers

  • It is SMALL. Some loggers really go overboard but I need this stuff to be tiny. 1K is about all I want to spend on a logging lib
  • It supports levels. Levels make logging useful!
  • It has AWESOME debug features. Just set DEBUG=module1,module2 and these modules will start logging debug info
  • By default, only Error and Warning message will show up in the console in browsers, meaning you can log as much as you want and only those people that are interested in it will actually see it. You can just leave your log statements in your production code. In Node JS we use INFO as the default level because there the 'users' are mostly developers / server admins etc who are more interested in our logging. Using different defaults on different platforms felt weird at first but it actually works out great for my projects.
  • It supports a shorthand form that applies formatting.

Example usage 

var ulog = require('ulog')
var log = ulog('my-module')

log.debug('Debug message');
log.info('Info message');
log.warn('Warning message');
log('Formatted message (at debug level)')
log('warn', 'Formatted message (at warning level)')
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Yields (on browsers)

Warning message
21:23:24   .03 my-module                Formatted message (at warning level)
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If you want to try it

Now is the perfect time as I am trying to perfect v2 currently. So if you want to try this, please install the beta and let me know:

npm install --save ulog@beta
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Or you can use v1, but that version is more limited in features:

npm install --save ulog
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entrptaher profile image
Md. Abu Taher πŸ‘¨β€πŸ’» • • Edited