Feature request: support `CRITICAL` log level

[H1Gdev]

Use case

I would like to monitor lambda function logs by level key. (using Amazon CloudWatch)

In another lambda function(using Python), ERROR and CRITICAL are already used properly, so I would like to use them differently in new lambda function(using Node.js) under the same conditions.

Node.js and Java do not provide critical level.

Ref. #1392

Solution/User Experience

• Add CRITICAL.
• Add critical method in Logger class.

Alternative solutions

No response

Acknowledgment

• This feature request meets Lambda Powertools Tenets
• Should this be considered in other Lambda Powertools languages? i.e. Python, Java, and .NET

Future readers

Please react with 👍 and your use case to help us understand customer demand.

[dreamorosi]

Hi @H1Gdev thank you for taking the time to open this feature request following our previous discussion.

For the benefit of future readers, I'll include here my initial response as for why Powertools for Python supports this log level while this library doesn't:

Powertools for Python builds on top of Python's logging module that is part of the standard library. As such, that version of Powertools supports the same levels that the logging module supports:

Level	Numeric Value
CRITICAL	50
ERROR	40
WARNING	30
INFO	20
DEBUG	10
NOTSET	0

Node.js on the other hand, deals with logs differently and doesn't have a strict level structure like Python does. The closest thing to Python's logging library in Node.js is the Console object.

The Console object does have some methods like info, debug, warn, error, etc. but doesn't have a concept of levels, and most importantly for this discussion, doesn't have a method that maps to CRITICAL. In Node.js, using one method or the other only influences whether the log will be emitted to stdout or stderr with warn and error going to stderr and all others going to stdout.

In Powertools for Typescript however the log level doesn't just influence the which Console method will be used to log, but it also influences the fact that logs will contain a level key (see docs).

---

While as mentioned the log level doesn't have a correspondent in Node.js, I see value in aligning the output of Logger between this library with the Python version. In this way, users who operate functions in both languages can use the same queries, dashboards, and alarms on these logs.

In our implementation, Logger will accept the CRITICAL log level which under the hood will map to console.error and emit to stderr. From the log and output perspective there will be no difference between calling logger.error and logger.critical except for the fact that the latter will contain level: "CRITICAL" as key.

I'll move this to the backlog to be implemented.

[github-actions]

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