Introduction to Node.js Debugging

Julián Duque

Developer and Educator

@julian_duque

https://twitch.tv/julianduque

Challenges

• Debugging Asynchronous workflows add a layer of complexity
• Post-mortem debugging requires C/C++ tooling skills

How to debug Node.js Applications?

Choose your weapon!

Node Inspect

• node --inspect

• node --inspect-brk

• Go to

  • chrome://inspect

• Click on Inspect

Some tips

• Start debug on a running process with:

  • kill -USR1 <pid>

• Add a breakpoint to your code using:

  • debugger;

VSCode

Visual Studio Code supports the Node.js Debug protocol and it is a great tool for local and remote debugging.

ndb

It is a Chromium-based, standalone Node.js debugger by the ChromeLabs team with extra features that Chrome Inspector doesn't support out of the box

• Child Process Debugging
• Blackboxing
• Edit in Place

$ npm install -g ndb

llnode

• Useful for Post-Mortem debugging
• Get useful information from a coredump after a crash
• It helps to see the state of the Node process and debug the C/C++ native layer

https://github.com/nodejs/llnode

• npm install -g llnode

• llnode `which node` -c core.dump

https://asciinema.org/a/29589

Useful npm modules

debug

Allows you to have a console-based debugger that can be enabled by using an environment variable

$ npm install debug

trace & clarify

trace: Augment your async stack traces

clarify: Removes node internals

$ npm i --save trace clarify

$ node --stack_trace_limit=100 -r trace server.js

$ node --stack_trace_limit=100 -r trace -r clarify server.js

Thank you!