Fix Frontend Runtime Errors

Fix Frontend Runtime Errors

Purpose

Resolve frontend runtime errors (console exceptions, blank screens, broken interactions) with a structured triage and evidence-backed verification.

When to use

Use this skill when:

• The UI shows a runtime exception in the console
• A page renders blank or crashes after navigation
• A runtime error occurs after a data/backend change
• Async errors are not handled gracefully (unhandled rejections)

Inputs

• Error message + stack trace (copy/paste)
• Steps to reproduce (route, clicks, input values)
• Environment details (browser, build, feature flags)
• Relevant network logs (redact secrets)

Outputs

• Root cause analysis (where and why)
• Minimal code fix (and optional improvement suggestions)
• Verification evidence (what was tested and expected outcomes)

Steps

1. Reproduce reliably
   • Confirm the reproduction steps and the exact error.
2. Capture diagnostics
   • console error + stack trace
   • failing network request(s) and response shape
   • relevant UI state at time of failure
   • Use the bug report capture template to keep the evidence structured.
3. Classify the failure mode
   • rendering error (null/undefined access)
   • data contract mismatch (backend response changed)
   • routing error (missing params)
   • async error handling (promise rejection)
   • environment/build mismatch (stale assets)
4. Apply a minimal fix
   • add guards and safe defaults where appropriate
   • correct data mapping at boundaries (normalize inputs)
   • ensure error UI (error boundary or safe fallback) where needed
   • avoid “catch and ignore” patterns
5. Verify
   • reproduction steps no longer fail
   • related flows still work
   • loading/error states render correctly
   • no new console errors introduced
6. Regression prevention (recommended)
   • add a test (unit/integration/e2e) or a contract assertion near the boundary

Verification

• Reproduction steps no longer produce the error
• Root cause explains the stack trace and observed state
• Fix is minimal and targeted (no unrelated refactors)
• Related flows still work correctly
• Loading states render appropriately
• Error states render with user-safe messages
• No new console errors introduced

Boundaries

• MUST NOT swallow errors without visibility (log/track unexpected failures)
• MUST NOT expose raw error details to end users
• MUST NOT record secrets/tokens in bug evidence
• SHOULD NOT guess at root cause without capturing diagnostics
• SHOULD prefer user-safe error UI plus logging/tracking for unexpected failures

Included assets

• Templates: ./templates/bug-report-template.md is a bug report capture format.
• Examples: ./examples/ includes a null/undefined access regression walkthrough.