Problem description:

const data = {'message':'hello'}
logger.log(data)
// now data contains "level":"info"

.info(), and probably other methods modify original object when the object contains 'message' field.
This is unfortunate because a user might be unaware of such behaviour, and can easily overlook this moment, which would lead to hard-to-find problems.

Possible fix:

Leave everything as it is (as user expect to pass config object to the logging method), but clone incoming object.

• winston version - (3.2.1)
• platform: all
• languages: all