Systematic Debugging Strategy

Initial Assessment

Before diving in, gather context:

• What changed? - Recent code changes, deployments, dependencies

• When did it start? - Timeline helps narrow scope

• Reproducible? - Consistent vs intermittent affects approach

• Error messages? - Exact text, stack traces, logs

• Environment? - Dev/staging/prod, OS, versions

Debugging Hierarchy (Work Through In Order)

1. Read the Error Message

• Parse the FULL stack trace

• Note the originating file and line number

• Look for "Caused by" chains

• Search error message verbatim if unclear

2. Reproduce Locally

• Create minimal reproduction case

• Isolate variables (data, environment, timing)

• Add logging at key points

3. Binary Search the Problem

• Comment out half the code

• Does it still fail? Problem is in remaining half

• Repeat until isolated

4. Check the Obvious

• Is it saved? Is it deployed?

• Correct environment variables?

• Dependencies installed/updated?

• Cache cleared?

• Correct branch?

5. Trace Data Flow

• Log inputs at entry point

• Log outputs at each transformation

• Find where actual diverges from expected

Common Bug Patterns

Symptom Likely Causes

Works locally, fails in prod Env vars, paths, permissions, CORS

Intermittent failure Race condition, caching, timing

Undefined/null error Missing data, async timing, typo

Silent failure Swallowed exception, wrong error handler

Performance degradation N+1 queries, memory leak, missing index

Debug Tools by Domain

JavaScript/React:

• Browser DevTools (Console, Network, React DevTools)

• console.log , console.table , debugger

• React Query DevTools, Redux DevTools

React Native:

• Flipper, React Native Debugger

• adb logcat (Android), Console.app (iOS)

• Remote JS debugging

Node.js:

• --inspect flag + Chrome DevTools

• DEBUG=* environment variable

• node --trace-warnings

Database:

• Query explain plans

• Slow query logs

• Connection pool monitoring

Output Format

When reporting findings:

• Root Cause - What actually caused the bug

• Fix - Code change required

• Prevention - How to avoid similar bugs

• Testing - How to verify the fix