Let's Debug Node.js Applications

Julián Duque

Lead Developer Advocate - Salesforce Heroku

@julian_duque

https://twitch.tv/julianduque

Mohith Shrivastava

Lead Developer Advocate - Salesforce

@msrivastav13

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 <script>

• node --inspect-brk <script>

• Go to

  • chrome://inspect

• Click on Inspect

Node Inspect

Node Inspect

Node Inspect

Some tips

• Start to debug on a running process with:

  • kill -USR1 <pid>

• Add a breakpoint to your code using a JS keyword:

  • debugger;

VSCode

Visual Studio Code supports the V8 inspector protocol and it is a great tool for local and remote debugging.

Other IDEs like WebStorm and Atom also support this protocol, use the tool you are most used to.

Some tips

• You can also add Logpoints from VS Code
• You can have multiple debugging configurations

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!