proc-log

proc-log

Emits 'log' events on the process object which a log output listener can consume and print to the terminal.

This is used by various modules within the npm CLI stack in order to send log events that can be consumed by a listener on the process object.

API

• log.error(...args) calls process.emit('log', 'error', ...args) The highest log level. For printing extremely serious errors that indicate something went wrong.
• log.warn(...args) calls process.emit('log', 'warn', ...args) A fairly high log level. Things that the user needs to be aware of, but which won't necessarily cause improper functioning of the system.
• log.notice(...args) calls process.emit('log', 'notice', ...args) Notices which are important, but not necessarily dangerous or a cause for excess concern.
• log.info(...args) calls process.emit('log', 'info', ...args) Informative messages that may benefit the user, but aren't particularly important.
• log.verbose(...args) calls process.emit('log', 'verbose', ...args) Noisy output that is more detail that most users will care about.
• log.silly(...args) calls process.emit('log', 'silly', ...args) Extremely noisy excessive logging messages that are typically only useful for debugging.
• log.http(...args) calls process.emit('log', 'http', ...args) Information about HTTP requests made and/or completed.
• log.pause() calls process.emit('log', 'pause') Used to tell the consumer to stop printing messages.
• log.resume() calls process.emit('log', 'resume') Used to tell the consumer that it is ok to print messages again.
• log.LEVELS an array of strings of all log method names

Examples

Every method calls process.emit('log', level, ...otherArgs) internally. So in order to consume those events you need to do process.on('log', fn).

Colorize based on level

Here's an example of how to consume proc-log events and colorize them based on level:

const chalk = require('chalk')

process.on('log', (level, ...args) => {
  if (level === 'error') {
    console.log(chalk.red(level), ...args)
  } else {
    console.log(chalk.blue(level), ...args)
  }
})

Pause and resume

pause and resume are included so you have the ability to tell your consumer that you want to pause or resume your display of logs. In the npm CLI we use this to buffer all logs on init until we know the correct loglevel to display. But we also setup a second handler that writes everything to a file even if paused.

let paused = true
const buffer = []

// this handler will buffer and replay logs only
// after `procLog.resume()` is called
process.on('log', (level, ...args) => {
  if (level === 'resume') {
    buffer.forEach((item) => console.log(...item))
    paused = false
    return
  } 

  if (paused) {
    buffer.push([level, ...args])
  } else {
    console.log(level, ...args)
  }
})

// this handler will write everything to a file
process.on('log', (...args) => {
  fs.appendFileSync('debug.log', args.join(' '))
})