Glen Arrowsmith
Feb 2018
Brisjs.com
twitter.com/garrows

Node.js Debugging

Node.js

LTS v8.9.4

The Lazy Way

console.log('A thing happened');

$ node app.js
A thing happened

Homework - console

The Better Lazy Way

const debug = require('util').debuglog('entity');

debug('A thing happened');


const debugEngine = require('util').debuglog('engine');

debugEngine('An engine thing');

$ node app.js
$ # nothing happened???
$ NODE_DEBUG=entity node app.js
ENTITY 21455: A thing happened
$ NODE_DEBUG=entity,engine node app
ENTITY 21497: A thing happened
ENGINE 21497: An engine thing

# Windows user?
set NODE_DEBUG=entity

Homework - Core Debug

Try setting NODE_DEBUG to a few of the

following to get core debug logs:

```
module
```
```
cluster
```
```
net
```
```
http
```
```
fs
```
```
tls
```
```
timers
```

... and checkout npmjs.com/package/debug

The Hard Way

console.log('Start');
for (var i = 0; i < 10; i++) {
  console.log('i', i);
  debugger;
}
console.log('End');

$ node debug app.js

The Old School Way

$ node --debug --debug-brk app.js
Debugger listening on [::]:5858

$ npm install -g node-inspector
$ node-inspector
Node Inspector v0.12.8
Visit http://127.0.0.1:8080/?port=5858 to start debugging.

$ node --debug --debug-brk app.js
Debugger listening on [::]:5858

The Cool Way

$ node --inspect --inspect-brk app.js
Debugger listening on ws://127.0.0.1:9229/09302d68-a88d-4fcf-a3e8-b00eb85b1d38
For help see https://nodejs.org/en/docs/inspector
Debugger attached.

chrome://inspect/