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Edge Case Handling and Debugging Questions

Covers the systematic identification, analysis, and mitigation of edge cases and failures across code and user flows. Topics include methodically enumerating boundary conditions and unusual inputs such as empty inputs, single elements, large inputs, duplicates, negative numbers, integer overflow, circular structures, and null values; writing defensive code with input validation, null checks, and guard clauses; designing and handling error states including network timeouts, permission denials, and form validation failures; creating clear actionable error messages and informative empty states for users; methodical debugging techniques to trace logic errors, reproduce failing cases, and fix root causes; and testing strategies to validate robustness before submission. Also includes communicating edge case reasoning to interviewers and demonstrating a structured troubleshooting process.

EasyTechnical
38 practiced
A 'Save' button's click handler isn't firing in production builds but works in development. Describe a step-by-step debugging process to reproduce and isolate the issue. Include checks for DOM overlays/z-index, CSS pointer-events, delegated event listeners, differences introduced by minification/tree-shaking, and how to produce a minimal reproducible case or collect production diagnostics.
HardTechnical
36 practiced
Your team shipped a release that improved feature X but caused a regression in the checkout flow affecting ~5% of users. As a senior frontend engineer, outline how you'd lead the postmortem: what data to collect, how to decide between hotfix vs rollback, how to prioritize engineering vs process fixes, how to communicate to stakeholders and customers, and which metrics to track to validate that the fixes worked.
EasyTechnical
42 practiced
You're given a header that unexpectedly wraps on small screens in Safari but not in Chrome. Outline a methodical debugging approach: the specific DevTools checks, CSS properties and vendor quirks to examine (e.g., -webkit-box, min-height, box-sizing, flex-basis), and propose at least two fixes or graceful fallbacks to make the layout consistent across WebKit and Blink engines.
EasyTechnical
43 practiced
Which automated and manual accessibility checks would you run to validate that form error messages are accessible to screen readers and keyboard users? Cover specific attributes (aria-describedby, role='alert', aria-invalid), focus management, and recommended tools (axe, Lighthouse), plus at least two manual screen reader checks and keyboard-only test cases.
HardTechnical
37 practiced
You receive a Sentry report referencing an uncaught production error in minified JS with no mapped stack frames (no source maps). Describe a step-by-step triage plan to resolve production-only minified errors: locate/rebuild/upload source maps, validate release mappings, enrich and capture breadcrumbs, reproduce with production bundles locally, and provide mitigations (feature flag rollback, hotfix) while fixing build/config.

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