level-change workaround doesn't work when once is used instead of on

[bienzaaron]

There is a workaround for the level-change event described here, which allows users to ignore level-change events created by child loggers. It appears this doesn't work when using once instead of on.

Working code (Using on)

The given code sample using on works fine:

const logger = require('pino')()
logger.on('level-change', function myHandler(lvl, val, prevLvl, prevVal) {
  if (logger !== this) {
    return
  }
  console.log('%s (%d) was changed to %s (%d)', prevLvl, prevVal, lvl, val)
})
logger.child({}); // trigger an event by creating a child instance, notice no console.log
logger.level = 'trace' // trigger event using actual value change, notice console.log

This correctly logs:

info (30) was changed to trace (10)

Not working code (Using once)

The same thing does NOT work when replacing on with once:

const logger = require('pino')()
logger.once('level-change', function myHandler(lvl, val, prevLvl, prevVal) {
  if (logger !== this) {
    return
  }
  console.log('%s (%d) was changed to %s (%d)', prevLvl, prevVal, lvl, val)
  logger.once('level-change', myHandler)
})
logger.child({});
logger.level = 'trace'

This incorrectly logs:

info (30) was changed to info (30)
info (30) was changed to trace (10)

[bienzaaron]

It looks like using on with options {once: true} works as well, but pino's types don't allow passing of the options object:

pino/pino.d.ts

Line 99 in 5aec425

on(event: "level-change", listener: pino.LevelChangeEventListener): this;

Edit: nevermind, it just doesn't respect the options param.

[mcollina]

I don't think there is much we can do about this. We do not override once or on and this looks like behavior inherited from Node.js core. What we could do is to include the actual logger as an argument. Would that be enough to fix your problem?

[bienzaaron]

Ah, I see. I think that should work. I can work on a PR to add it as an argument.

[github-actions]

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