January 08, 2020

util.debuglog

Today I wanted to add debug logs to the turbine project. This means that when a certain environment flag is set, extra info is printed to the console to aid debugging.

I have previously used the debug package for this, but I was wondering what other options.

I searched the internet for “debug log sindresorhus” and came across his repo: https://github.com/sindresorhus/debug-log - which happens to be deprecated, but alerted me to the existence of util.debuglog.

The builtin util package has a bunch of great functions in it, like promisify and inspect — and also the method debuglog.

You can read the official Node.js docs for it here: https://nodejs.org/api/util.html#util_util_debuglog_section

// index.js
const { debuglog } = require('util')

const log = debuglog('myapp')

log('doing the thing')

If you run the app normally, nothing is printed:

node ./index.js

But if you set the NODE_DEBUG flag to myapp then we see the log message!

NODE_DEBUG=myapp node./index.js
MYAPP 735650: doing the thing