lalog

Logging aggregation and distribution

Installation

npm i lalog --save

Usage

Setup

If logging to Loggly then your Loggly token needs to be set in the LOGGLY_TOKEN environment variable.

If you want to specify a different initial logging level for your application than the default error levels you can set the LALOG_LEVEL environment variable.

Create a Logger

Require the Logger class:

const Logger = require('lalog');

Set the logging level

Logger.setLevel('info');

There are 6 levels:

trace, info, warn, error, fatal, security

If you do not call setLevel(...) then it will default to error and above.

setLevel can be used to change the log level at anytime while your app is running and it will immediately change the level for any loggers that have been created.

Create a logger

const logger = Logger.create({
  serviceName: 'service-name',
  moduleName: 'module-name',
  presets: {}, // optional
  addTrackId: true, // options
});

or

const logger = new Logger({
  serviceName: 'service-name',
  moduleName: 'module-name',
  presets: {}, // optional - defaults to empty object if missing or not a valid object
  addTrackId: true, // optional - defaults to false
  isTransient: true, // optional - defaults to false
});

Notes on create:

• presets is an optional object that will have its contents merged with any object that's logged. Useful for putting in data that you want logged with every message.
• If addTrackId is truthy then a trackId (uuid) will be added to presets.
• The moduleName is added to presets as module.
• If isTransient is set to true then all calls to logger will be saved and written in batch mode, in sequence, to the destination if any of the log calls triggers a write. This flag is called isTransient because typically you will only use it for short lived transient loggers. The typical use case is when you attach a logger to the req/request object in a web request. You would then probably call the logger with trace, info and warn calls that would not be written if your level is set to error. If error() is called you would also want all the previous logs to be written so that you can see what happened before the error() was called. The isTransient flag causes the logger to store all of those logs and write then in this scenario.
  • More notes on isTransient
  • You would almost always want to also set trackId to true when you set isTransient to true so that you can easily find/filter the associated log messages.
  • You don't want to use this for long lived loggers as they may accumulate too many logs (local memory issues) and if the log messages are too big then they may error when writing to the destination.
  • Possible future feature is to provide a maximum number of log messages to accumulate if isTransient is set.

Write Log Messages

logger.trace({
  message: 'I am a message'
});

There are 6 levels at which to write log messages:

trace, info, warn, error, fatal, security

The log will only be written to the destination if the log level has be set at this or above. It defaults to error if not set.

The only parameter you can pass to logger.<level>() is an object which will be written to the destination after some modifications have been made to it:

• If the log is error or above then the object will be written to the destination.

time(label) and timeEnd(label, [logObject])

time() and timeEnd() work pretty much the same as console.time() and console.timeEnd().

time('label') starts the timer and timeEnd('label') stops the timer and writes the log.

timeEnd() operates at the info level. i.e. it will only write to the destination if the level is set to info or trace.

timeEnd has the same modifiers that a created logger has inasmuch as it can be called as:

time('label');
// do some stuff
timeEnd.warn('label');
// or
timeEnd.error('label');

timeEnd() and timeEnd.<level>() take an optional log object.

This allows you to do:

try {
  logger.time('write-to-db');
  await writeToDb();
  logger.timeEnd('write-to-db');
} catch(err) {
  logger.timeEnd.error('write-to-db', { err });
}

This saves you from having to do a logger.error() and a logger.timeEnd() if an error is caught. Also if the level is set to error then the timing will be captured in the event of an error (in addition to any extra logging data) but not in the event of normal operation because the default level for logger.timeEnd() is info.