Transform debugging from frustrating guesswork into systematic problem-solving with proven strategies, powerful tools, and methodical approaches.
\n1. Observe: What's the actual behavior?\n2. Hypothesize: What could be causing it?\n3. Experiment: Test your hypothesis\n4. Analyze: Did it prove/disprove your theory?\n5. Repeat: Until you find the root cause
\nDon't Assume:
\nDo:
\nExplain your code and problem out loud (to a rubber duck, colleague, or yourself). Often reveals the issue.
\n## Reproduction Checklist\n\n1. **Can you reproduce it?**\n - Always? Sometimes? Randomly?\n - Specific conditions needed?\n - Can others reproduce it?\n\n2. **Create minimal reproduction**\n - Simplify to smallest example\n - Remove unrelated code\n - Isolate the problem\n\n3. **Document steps**\n - Write down exact steps\n - Note environment details\n - Capture error messages\n## Information Collection\n\n1. **Error Messages**\n - Full stack trace\n - Error codes\n - Console/log output\n\n2. **Environment**\n - OS version\n - Language/runtime version\n - Dependencies versions\n - Environment variables\n\n3. **Recent Changes**\n - Git history\n - Deployment timeline\n - Configuration changes\n\n4. **Scope**\n - Affects all users or specific ones?\n - All browsers or specific ones?\n - Production only or also dev?\n## Hypothesis Formation\n\nBased on gathered info, ask:\n\n1. **What changed?**\n - Recent code changes\n - Dependency updates\n - Infrastructure changes\n\n2. **What's different?**\n - Working vs broken environment\n - Working vs broken user\n - Before vs after\n\n3. **Where could this fail?**\n - Input validation\n - Business logic\n - Data layer\n - External services\n## Testing Strategies\n\n1. **Binary Search**\n - Comment out half the code\n - Narrow down problematic section\n - Repeat until found\n\n2. **Add Logging**\n - Strategic console.log/print\n - Track variable values\n - Trace execution flow\n\n3. **Isolate Components**\n - Test each piece separately\n - Mock dependencies\n - Remove complexity\n\n4. **Compare Working vs Broken**\n - Diff configurations\n - Diff environments\n - Diff data\n// Chrome DevTools Debugger\nfunction processOrder(order: Order) {\n debugger; // Execution pauses here\n\n const total = calculateTotal(order);\n console.log(\"Total:\", total);\n\n // Conditional breakpoint\n if (order.items.length > 10) {\n debugger; // Only breaks if condition true\n }\n\n return total;\n}\n\n// Console debugging techniques\nconsole.log(\"Value:\", value); // Basic\nconsole.table(arrayOfObjects); // Table format\nconsole.time(\"operation\");\n/* code */ console.timeEnd(\"operation\"); // Timing\nconsole.trace(); // Stack trace\nconsole.assert(value > 0, \"Value must be positive\"); // Assertion\n\n// Performance profiling\nperformance.mark(\"start-operation\");\n// ... operation code\nperformance.mark(\"end-operation\");\nperformance.measure(\"operation\", \"start-operation\", \"end-operation\");\nconsole.log(performance.getEntriesByType(\"measure\"));\nVS Code Debugger Configuration:
\n// .vscode/launch.json\n{\n \"version\": \"0.2.0\",\n \"configurations\": [\n {\n \"type\": \"node\",\n \"request\": \"launch\",\n \"name\": \"Debug Program\",\n \"program\": \"${workspaceFolder}/src/index.ts\",\n \"preLaunchTask\": \"tsc: build - tsconfig.json\",\n \"outFiles\": [\"${workspaceFolder}/dist/**/*.js\"],\n \"skipFiles\": [\"<node_internals>/**\"]\n },\n {\n \"type\": \"node\",\n \"request\": \"launch\",\n \"name\": \"Debug Tests\",\n \"program\": \"${workspaceFolder}/node_modules/jest/bin/jest\",\n \"args\": [\"--runInBand\", \"--no-cache\"],\n \"console\": \"integratedTerminal\"\n }\n ]\n}\n# Built-in debugger (pdb)\nimport pdb\n\ndef calculate_total(items):\n total = 0\n pdb.set_trace() # Debugger starts here\n\n for item in items:\n total += item.price * item.quantity\n\n return total\n\n# Breakpoint (Python 3.7+)\ndef process_order(order):\n breakpoint() # More convenient than pdb.set_trace()\n # ... code\n\n# Post-mortem debugging\ntry:\n risky_operation()\nexcept Exception:\n import pdb\n pdb.post_mortem() # Debug at exception point\n\n# IPython debugging (ipdb)\nfrom ipdb import set_trace\nset_trace() # Better interface than pdb\n\n# Logging for debugging\nimport logging\nlogging.basicConfig(level=logging.DEBUG)\nlogger = logging.getLogger(__name__)\n\ndef fetch_user(user_id):\n logger.debug(f'Fetching user: {user_id}')\n user = db.query(User).get(user_id)\n logger.debug(f'Found user: {user}')\n return user\n\n# Profile performance\nimport cProfile\nimport pstats\n\ncProfile.run('slow_function()', 'profile_stats')\nstats = pstats.Stats('profile_stats')\nstats.sort_stats('cumulative')\nstats.print_stats(10) # Top 10 slowest\n// Delve debugger\n// Install: go install github.com/go-delve/delve/cmd/dlv@latest\n// Run: dlv debug main.go\n\nimport (\n \"fmt\"\n \"runtime\"\n \"runtime/debug\"\n)\n\n// Print stack trace\nfunc debugStack() {\n debug.PrintStack()\n}\n\n// Panic recovery with debugging\nfunc processRequest() {\n defer func() {\n if r := recover(); r != nil {\n fmt.Println(\"Panic:\", r)\n debug.PrintStack()\n }\n }()\n\n // ... code that might panic\n}\n\n// Memory profiling\nimport _ \"net/http/pprof\"\n// Visit http://localhost:6060/debug/pprof/\n\n// CPU profiling\nimport (\n \"os\"\n \"runtime/pprof\"\n)\n\nf, _ := os.Create(\"cpu.prof\")\npprof.StartCPUProfile(f)\ndefer pprof.StopCPUProfile()\n// ... code to profile\n# Git bisect for finding regression\ngit bisect start\ngit bisect bad # Current commit is bad\ngit bisect good v1.0.0 # v1.0.0 was good\n\n# Git checks out middle commit\n# Test it, then:\ngit bisect good # if it works\ngit bisect bad # if it's broken\n\n# Continue until bug found\ngit bisect reset # when done\nCompare working vs broken:
\n## What's Different?\n\n| Aspect | Working | Broken |\n| ------------ | ----------- | -------------- |\n| Environment | Development | Production |\n| Node version | 18.16.0 | 18.15.0 |\n| Data | Empty DB | 1M records |\n| User | Admin | Regular user |\n| Browser | Chrome | Safari |\n| Time | During day | After midnight |\n\nHypothesis: Time-based issue? Check timezone handling.\n// Function call tracing\nfunction trace(\n target: any,\n propertyKey: string,\n descriptor: PropertyDescriptor,\n) {\n const originalMethod = descriptor.value;\n\n descriptor.value = function (...args: any[]) {\n console.log(`Calling ${propertyKey} with args:`, args);\n const result = originalMethod.apply(this, args);\n console.log(`${propertyKey} returned:`, result);\n return result;\n };\n\n return descriptor;\n}\n\nclass OrderService {\n @trace\n calculateTotal(items: Item[]): number {\n return items.reduce((sum, item) => sum + item.price, 0);\n }\n}\n// Chrome DevTools Memory Profiler\n// 1. Take heap snapshot\n// 2. Perform action\n// 3. Take another snapshot\n// 4. Compare snapshots\n\n// Node.js memory debugging\nif (process.memoryUsage().heapUsed > 500 * 1024 * 1024) {\n console.warn(\"High memory usage:\", process.memoryUsage());\n\n // Generate heap dump\n require(\"v8\").writeHeapSnapshot();\n}\n\n// Find memory leaks in tests\nlet beforeMemory: number;\n\nbeforeEach(() => {\n beforeMemory = process.memoryUsage().heapUsed;\n});\n\nafterEach(() => {\n const afterMemory = process.memoryUsage().heapUsed;\n const diff = afterMemory - beforeMemory;\n\n if (diff > 10 * 1024 * 1024) {\n // 10MB threshold\n console.warn(`Possible memory leak: ${diff / 1024 / 1024}MB`);\n }\n});\n## Strategies for Flaky Bugs\n\n1. **Add extensive logging**\n - Log timing information\n - Log all state transitions\n - Log external interactions\n\n2. **Look for race conditions**\n - Concurrent access to shared state\n - Async operations completing out of order\n - Missing synchronization\n\n3. **Check timing dependencies**\n - setTimeout/setInterval\n - Promise resolution order\n - Animation frame timing\n\n4. **Stress test**\n - Run many times\n - Vary timing\n - Simulate load\n## Performance Debugging\n\n1. **Profile first**\n - Don't optimize blindly\n - Measure before and after\n - Find bottlenecks\n\n2. **Common culprits**\n - N+1 queries\n - Unnecessary re-renders\n - Large data processing\n - Synchronous I/O\n\n3. **Tools**\n - Browser DevTools Performance tab\n - Lighthouse\n - Python: cProfile, line_profiler\n - Node: clinic.js, 0x\n## Production Debugging\n\n1. **Gather evidence**\n - Error tracking (Sentry, Bugsnag)\n - Application logs\n - User reports\n - Metrics/monitoring\n\n2. **Reproduce locally**\n - Use production data (anonymized)\n - Match environment\n - Follow exact steps\n\n3. **Safe investigation**\n - Don't change production\n - Use feature flags\n - Add monitoring/logging\n - Test fixes in staging\n## When Stuck, Check:\n\n- [ ] Spelling errors (typos in variable names)\n- [ ] Case sensitivity (fileName vs filename)\n- [ ] Null/undefined values\n- [ ] Array index off-by-one\n- [ ] Async timing (race conditions)\n- [ ] Scope issues (closure, hoisting)\n- [ ] Type mismatches\n- [ ] Missing dependencies\n- [ ] Environment variables\n- [ ] File paths (absolute vs relative)\n- [ ] Cache issues (clear cache)\n- [ ] Stale data (refresh database)\n