Feature request: Add ability to "eject" a set of debug logs

[karimsa]

The current pattern of explicitly enabling debug logs via the DEBUG= environment variable works well for server environments. But when using the debug module in a test environment or with a CLI, it is helpful to be able to "eject" a set of debug logs into either a log file or to send them remotely to a bug tracker.

A good example of this is how npm runs silently (usually), but on failure, it generates a npm-debug.log file in the working directory with its hidden debug log messages. It would be nice to have this as a built-in feature in debug rather than implementing it in each individual use case.

I could possibly open a PR for this after some discussion around the API/design - if this seems like a feature that you would like to have in debug

[Qix-]

Could you better explain what you mean by this? You mean you want to redirect certain namespaces to different places (e.g. a file)?

[karimsa]

Yeah, pretty much. Something like this:

https://github.com/hoppjs/hopp/blob/master/packages/hopp/src/utils/log.js#L86

https://github.com/hoppjs/hopp/blob/master/packages/hopp/src/utils/log.js#L127

But pushing into an array is a terrible idea (unless there is a max size).

[karimsa]

The equivalent of something like this:

const debug = require('debug')('my-app')
const fs = require('fs')

const logFile = fs.createReadStream('my-app-debug.log')
debug.log = msg => logFile.write(`${msg}\n`)

But there are a few issues with this:

• Can't redirect logs that don't belong to this logger
  • i.e. every module in our app currently creates different namespaces but following the pattern foko:... so I'd like to be able to just say foko:* -> log-file in a single place instead of doing this per-file.
  • also want to be able to redirect logs from other 3rd party namespaces like nightmare

---

Perhaps something along these lines:

const createDebugger = require('debug')
const debug = createDebugger('my-app')

createDebugger.stream(['my-app:*', 'nightmare'])
  .pipe(fs.createReadStream('my-app-debug.log'))

[Qix-]

See #556 :)