lambda-log

lambda-log

A Node.js package to facilitate and enforce logging standards from processes and applications running within Lambda Functions, various AWS Services, and wherever JSON logs are desired. Lambda Log formats your log messages as JSON for simple parsing and filtering within tools such as CloudWatch Logs. Supports Node 10+.

This module is not just for Lambda! You can use this is many different environments that support reading JSON from logs. While the name remains lambda-log, it's really a universal JSON logger.

Why another lambda logger? There are others out there, but seemed to be convoluted, included more functionality than needed, not maintained, or not configurable enough. I created lambda-log to include the important functionality from other loggers, but still keeping it simple with minimal dependencies.

Features

Anyone can log JSON to the console, but with Lambda Log you also get:

• Metadata and tags that may be set globally or individually for each log message.
• Error and Error-like objects logged include stacktraces in the metadata automatically.
• Each log message emits an event to allow third-party integration.
• Pluggable and customizable by extending the LambdaLog class.
• Pretty-printing of the JSON log message in dev mode.
• Well documented, commented, and maintained source code.
• Over 1 million downloads and more than 20k weekly downloads.
• Small footprint.

New in Version 3.0.0

Version 3.0.0 of Lambda Log brings a bunch of changes, new features, and a new website.

Broad Changes:

• Refactor all code to meet new ESLint specifications and to stay up-to-date with newer ecmascript specifications.
• New website with better documentation.
• Tests are now using Jest instead of Mocha.
• Switched from TravisCI to Github Actions.

New Features:

• Added levelKey configuration option to be able to change the key name for log levels.
• Added messageKey configuration option to be able to change the key name for log messages.
• Added tagsKey configuration option to be able to change the key name for tags.
• Added ability to remove log level and tags from the outputted log JSON.
• Added addLevel() method to quickly add a custom log level to an instance of LambdaLog.
• Tags can now be functions that return a dynamic tag for log messages.
• Tags now have variable support.
• Tags that are null, undefined or "" are now removed from the tags array.
• Metadata that contains Error objects are now automatically converted to a plain object.

Breaking Changes:

• All of the private properties of both the LambdaLog and LogMessage classes are stored using Symbols. This may break some advanced uses of Lambda Log from version 2.
• Tags no longer contain any default, built-in tags and are empty by default.
• Some of the properties of LogMessage have been moved from the constructor to their own getter functions.

Documentation

Documentation for Lambda Log has moved to our new website.

Tests

See Development Documentation.

Contributing

See Contributing Documentation.

License

MIT License. See License in the repository.

Changelog

3.0.0 (2021-04-12)

Bug Fixes

• add .npmignore file to help reduce the size of the package (c21bd7f)
• add .npmignore file to help reduce the size of the package (9ccdc69)
• do not use husky when on a CI environment (a17ac76)
• reverse the check for LAMBDALOG_SILENT env variable (95828b1)
• reverse the check for LAMBDALOG_SILENT env variable (5ab6dc5)

Code Refactoring

• move message.tags to a getter and setter (201a6fe)

Features

• add ability for tags to be functions (459380f)
• add ability for tags to be functions (87ea24d)
• add ability to change the key names of the message output (4a71909)
• add ability to change the key names of the message output (bc1169b)
• add new method addLevel() to LambdaLog (9fde2e3)
• add new method addLevel() to LambdaLog (f7dbfd0)
• add new options levelKey, messageKey, and tagsKey (bb5ba70)
• add new options levelKey, messageKey, and tagsKey (4d10968)
• add new website! (44a15dc)
• add new website! (9aa6e2e)
• add symbols for referencing private properties in LogMessage (f4b1c99)
• add symbols for referencing private properties in LogMessage (beb5e39)
• add symbols to reference certain private properties (b502366)
• add symbols to reference certain private properties on LogMessage class (952b62d)
• convert Errors in metadata to plain objects #31 (f55d474)
• convert Errors in metadata to plain objects #31 (576052a)
• remove default tags and add tag variable support #29 (a43b0ae)
• remove default tags and add tag variable support #29 (ae686ef)
• set node engine to >= 10.0.0 (0b5e564)
• set node engine to >= 10.0.0 (2d022ec)
• switch from travis to github actions (6ca053f)
• use jest for testing and coverage (216141d)
• internal: add function to stub errors with a toJSON method (b5e3dbe)
• switch from travis to github actions (f2d418e)
• use jest for testing and coverage (fafed5d)
• internal: add function to stub errors with a toJSON method (d0707bd)

BREAKING CHANGES

• There are no longer any built-in tags added to the tags array for each log message.
• message.tags is no longer a property of the LogMessage class that can be directly changed.
• Whenever an Error object is passed into the metadata for a log message, it will automatically be converted to a plain object as stringifying the an Error object will always yield {}.
• Previously you could directly access the private properties of LogMessage. In order to add some integrity, they are no longer using standard property names starting with an underscore and are instead referenced using symbols instead. For advanced usage, these symbols are exported as a static property on the LogMessage class under LogMessage.symbols.
• Previously you could directly access the private properties of LambdaLog. In order to add some integrity, they are no longer using standard property names starting with an underscore and are instead referenced using symbols instead. For advanced usage, these symbols are exported as a static property on the LambdaLog class under LambdaLog.symbols.