Add a basic formatters option to the browser pino

[KatelynKim]

Description

Add a basic formatters option to the browser implementation of pino with the ability to format the level object. The formatting behavior for the level object should mirror that of the non-browser implementation.

This was requested in #1891.

Testing with Next.js

1. Create a basic Next.js app: npx create-next-app@latest.
2. Link your app to the current version of the pino package (I use yalc for this)
3. Add a basic logger with browser.formatters.level option supplied:

// src/logger.js
import pino from 'pino'

const logger = pino({ 
  browser: {
    formatters: {
      level (label, number) {
        return { label, level: number}
      }
    }
  }
})

export default logger

4. Create a basic middleware

// src/middleware.js

import { NextResponse } from 'next/server'
import logger from './logger'

export function middleware(request) {
  logger.info('I am logging a message from the middleware')
  return NextResponse.next()
}

5. Run the app and check the terminal for the correct log format. For the above example, it should look like:

{
  time: 1707198967745,
  label: 'info',
  level: 30,
  msg: 'I am logging a message from the middleware'
}

[mcollina]

lgtm

[KatelynKim]

lgtm

Thanks for the approval! I just synced the forked repo and would need your approval to run the workflows.
Could I also get write access to merge the repo when the workflows pass?

[mcollina]

lgtm

[KatelynKim]

lgtm

Thanks once again. How could I get the PR merged?

[mcollina]

i’ll ship it ;)