abdulyasir100 debug-pro
Systematic debugging methodology and language-specific debugging commands.
The 7-Step Debugging Protocol
- Reproduce - Get it to fail consistently. Document exact steps, inputs, and environment.
- Isolate - Narrow scope. Comment out code, use binary search, check recent commits with
git bisect. - Hypothesize - Form a specific, testable theory about the root cause.
- Instrument - Add targeted logging, breakpoints, or assertions.
- Verify - Confirm root cause. If hypothesis was wrong, return to step 3.
- Fix - Apply the minimal correct fix. Resist the urge to refactor while debugging.
- Regression Test - Write a test that catches this bug. Verify it passes.
Language-Specific Debugging
JavaScript / TypeScript
node --inspect-brk app.js # Node.js debugger
# Chrome DevTools: chrome://inspect
console.log(JSON.stringify(obj, null, 2))
console.trace('Call stack here')
console.time('perf'); /* code */ console.timeEnd('perf')
node --expose-gc --max-old-space-size=4096 app.js # Memory leaks
Python
python -m pdb script.py # Built-in debugger
breakpoint() # Python 3.7+
python -X tracemalloc script.py # Verbose tracing
python -m cProfile -s cumulative script.py # Profile
Swift
lldb ./MyApp
(lldb) breakpoint set --name main
(lldb) run
(lldb) po myVariable
# Xcode: Product > Profile (Instruments)
CSS / Layout
* { outline: 1px solid red !important; }
.debug { background: rgba(255,0,0,0.1) !important; }
Network
curl -v https://api.example.com/endpoint
dig example.com
nslookup example.com
lsof -i :3000
netstat -tlnp
Git Bisect
git bisect start
git bisect bad # Current commit is broken
git bisect good abc1234 # Known good commit
# Test middle commit, then: git bisect good / git bisect bad
# Repeat until root cause found
git bisect reset
Common Error Patterns
| Error | Likely Cause | Fix |
|---|---|---|
Cannot read property of undefined |
Missing null check | Add optional chaining (?.) or validate data |
ENOENT |
File/directory doesn't exist | Check path, create directory |
CORS error |
Backend missing CORS headers | Add CORS middleware |
Module not found |
Missing dependency or wrong path | npm install, check tsconfig paths |
Hydration mismatch (React) |
Server/client render different HTML | Use useEffect for client-only |
Segmentation fault |
Memory corruption, null pointer | Check array bounds, pointer validity |
Connection refused |
Service not running | Check if service is up, verify port/host |
Permission denied |
File/network permission issue | Check chmod, firewall, sudo |
Quick Diagnostic Commands
lsof -i :PORT # What's using this port?
ps aux | grep PROCESS # What's this process doing?
fswatch -r ./src # Watch file changes
df -h # Disk space
top -l 1 | head -10 # System resource usage