I think it should be this.log_level

[gobinath2389]

https://github.com/ishtms/learn-nodejs-hard-way/blame/051798fb90cf5c16e2bd7a0407df3b5931a06325/chapters/ch04-logtar-our-logging-library.md#L193

[Ishtmeet Singh]

The member variable is #level. The log_level was actually a typo from my side on the markdown/chapter. You can find the final code of that chapter here

Thanks. @gobinath2389