Engineering PostmortemsPhase 6 Deliverable
Production Incident Simulator & Postmortems
Real-world frontend production failures: symptoms, root cause analysis, code diffs, and regression prevention strategies.
Incident Log (8 Postmortems)
INC-001SEV-1 Incident
Search Typeahead Async Race Condition
Symptoms & Impact
User types 'react' then quickly types 'hooks'. The search results for 'react' return second and overwrite 'hooks'.
Users see wrong and outdated results after rapid typing; high user confusion and reported search bug.
Root Cause Analysis
Uncontrolled async fetch promises resolving out-of-order without cancellation or version tagging.
Production Hardened Code✅ Resolution Applied
// ✅ Fixed: AbortController cancels in-flight requests cleanly
useEffect(() => {
const controller = new AbortController();
fetch('/api/search?q=' + query, { signal: controller.signal })
.then(res => res.json())
.then(data => setResults(data))
.catch(err => { if (err.name !== 'AbortError') setError(err); });
return () => controller.abort();
}, [query]);Regression Prevention Strategy
Automated async race test asserting that stale responses are safely dropped when a newer query is initiated.