Debug Assistant

Systematic debugging methodology for quickly identifying and resolving code issues.

Debugging Framework

1. Understand the Problem

•What is the expected behavior?
•What is the actual behavior?
•When did it start failing?
•Is it reproducible?

2. Gather Information

•Full error message and stack trace
•Input data that triggers the issue
•Environment details (OS, runtime version, dependencies)
•Recent code changes

3. Form Hypotheses

•List possible causes
•Rank by likelihood
•Consider edge cases

4. Test Hypotheses

•Add logging/breakpoints
•Isolate the problem
•Binary search through code changes

5. Fix and Verify

•Implement fix
•Test the specific case
•Test related functionality
•Add regression test

Common Error Patterns

Null/Undefined Errors

JavaScript:

javascript

// Error: Cannot read property 'x' of undefined
// Solution: Optional chaining or null check
const value = obj?.nested?.property ?? defaultValue;

Python:

python

# AttributeError: 'NoneType' object has no attribute 'x'
# Solution: Check for None
value = obj.attr if obj is not None else default

Type Errors

TypeScript:

typescript

// Type 'string' is not assignable to type 'number'
// Solution: Type conversion or fix the type
const num: number = parseInt(stringValue, 10);

Python:

python

# TypeError: unsupported operand type(s)
# Solution: Ensure consistent types
result = int(a) + int(b)

Async/Await Issues

JavaScript:

javascript

// Common: Forgetting await
// Wrong
const data = fetchData(); // Returns Promise, not data
// Correct
const data = await fetchData();

// Common: Parallel vs Sequential
// Sequential (slow)
const a = await fetchA();
const b = await fetchB();
// Parallel (fast)
const [a, b] = await Promise.all([fetchA(), fetchB()]);

Python:

python

# Common: Mixing sync and async
# Wrong
def sync_function():
    await async_call()  # SyntaxError
# Correct
async def async_function():
    await async_call()

Memory Issues

Signs:

•Gradually increasing memory usage
•OutOfMemoryError
•Process killed by OS

Common causes:

•Unbounded caches/collections
•Event listener not removed
•Circular references
•Large objects in closures

Race Conditions

Signs:

•Intermittent failures
•Works in debugger, fails in production
•Different behavior under load

Solutions:

•Mutex/locks
•Atomic operations
•Message queues
•Idempotent operations

Stack Trace Analysis

JavaScript

code

TypeError: Cannot read property 'name' of undefined
    at getUserName (user.js:15:23)
    at processUser (handler.js:42:12)
    at main (index.js:8:5)

•Read bottom to top for call order
•Error location: user.js line 15, column 23
•Look for your code (not node_modules)

Python

code

Traceback (most recent call last):
  File "main.py", line 8, in <module>
    main()
  File "handler.py", line 42, in process_user
    get_user_name(user)
  File "user.py", line 15, in get_user_name
    return user.name
AttributeError: 'NoneType' object has no attribute 'name'

•Read top to bottom for call order
•Most specific error at bottom

Java

code

java.lang.NullPointerException
    at com.example.User.getName(User.java:15)
    at com.example.Handler.processUser(Handler.java:42)
    at com.example.Main.main(Main.java:8)

•Read top to bottom for location
•Check for "Caused by:" for root cause

Debugging Commands

Node.js

bash

# Debug mode
node --inspect app.js
# Chrome DevTools: chrome://inspect

# Memory snapshot
node --inspect --expose-gc app.js

Python

bash

# PDB debugger
python -m pdb script.py

# In code
import pdb; pdb.set_trace()  # Python 3.6-
breakpoint()  # Python 3.7+

General

bash

# Verbose logging
DEBUG=* node app.js
RUST_LOG=debug cargo run

Quick Fixes Checklist

• Restart the service/process
• Clear cache/rebuild
• Check environment variables
• Verify dependencies installed
• Check file permissions
• Review recent git commits
• Check logs for earlier errors
• Try in isolation (minimal reproduction)

References

See references/debugging_techniques.md for advanced debugging strategies.