Debugging

The essentials

• Reproducibility
• Reduction
• Experimentation
• ​Experience
• Tenacity

Techniques

• Interactive
• Print (or tracing)
• Remote 
• Post Mortem
• Wolf fence algorithm
• Delta debugging
• Saff Squeeze

Comparing Node.js Debug Options

1. Built-in Debugger

2. Node Inspector

3. IDE Debuggers

1. Built-in Debugger

"debugger" statement

run your app in debug mode via:

node debug  [your app]

setBreakpoint() – sb()
setBreakpoint(line) – sb(line)
clearBreakpoints() – cb()

repl , watch(expression)

continue – cont, c
step – next, n
step in – step, s
step out – out, o

node debug -p <pid> - Connects to the process via the pid

node debug <URI> - Connects to the process via the URI such as localhost:5858

run your app in debug mode via:

node --debug  [your app]

Attach Debugger

2. Node Inspector

Node Inspector allows you to use the DevTools user interface with the native Node debugger

npm install -g node-inspector

node-debug app.js

Problem:

The built-in Node debugger uses a protocol called V8-Debug

while DevTools uses the Chrome Debugging Protocol

Solution:

V8 Inspector Integration in Node.js v6.3+

node --inspect app.js

node --inspect=9222 app.js

Once you have found the bug

"Never leave an enemy at your back"