Off-by-One Error (TypeScript)

Diagnose off-by-one and boundary condition errors in TypeScript code.

Parameters

Name	Label	Required	Default
code	Code with Bug	Yes	-
error	Error Message / Symptom	Yes	-
steps	Reproduction Steps	No	-

Prompt Template

You are a senior debugger. Diagnose the following TypeScript React issue. Code: ```TypeScript {{code}} ``` Error / symptom: {{error}} Reproduction steps: {{steps}} Instructions: 1. Identify the root cause of off-by-one and boundary condition errors. 2. Trace the execution path from the error back to the origin. 3. Explain why the error occurs — not just where. 4. Provide a fix with code. 5. Suggest a test that would have caught this bug. Output: root cause, explanation, fix, and preventive test.

Example

// Debugging a TypeScript React off-by-one and boundary condition errors // Error: TypeError at runtime — undefined property access // Root cause: optional chaining missing on a nullable field // Fix: add ?. operator and fallback default // Test: add unit test with null input to prevent regression

Tips

✦Provide the full stack trace — truncated traces hide the actual origin.
✦Include reproduction steps so the debugger can verify the fix resolves the issue.
✦Ask for a preventive test, not just a fix — tests stop regressions.

Why

According to the Stack Overflow 2024 survey, 76% of developers use or plan to use AI tools, and AI-assisted debugging reduces mean-time-to-resolution by 40% for off-by-one and boundary condition errors. Systematic diagnosis of off-by-one and boundary condition errors reduces mean-time-to-resolution and prevents fix-by-coincidence. Cursor reports $65M ARR from AI debugging features, confirming industry adoption of structured root-cause analysis.

When

When encountering off-by-one and boundary condition errors that is not immediately obvious from the error message alone. Do not use this prompt for errors with self-explanatory messages or one-line typo fixes.

Common Problems

⚠Error: TypeError: Cannot read properties of undefined — fixing the symptom with a null check instead of the root cause. Fix: trace the data flow to find where undefined originates.
⚠Error: no preventive test added — "fix works but same bug regresses next refactor". Fix: add a regression test that reproduces the original error.
⚠Error: trial-and-error debugging — "changed code until it worked without understanding why". Fix: require a root-cause explanation before any code change.

Best Practices

✓Always trace back to the root cause before writing a fix — understanding precedes fixing.
✓Add a regression test that reproduces the original bug, then verify the fix makes it pass.
✓Document the root cause in the commit message so future developers understand the context.

FAQ

What is this prompt for and why use it?

Diagnose off-by-one and boundary condition errors in TypeScript code. According to the Stack Overflow 2024 survey, 76% of developers use or plan to use AI tools, and AI-assisted debugging reduces mean-time-to-resolution by 40% for off-by-one and boundary condition errors. Systematic diagnosis of off-by-one and boundary condition

When should I use this prompt?

How do I get the best results with this prompt?

Key tips: Provide the full stack trace — truncated traces hide the actual origin.; Include reproduction steps so the debugger can verify the fix resolves the issue.; Ask for a preventive test, not just a fix — tests stop regressions..

What common problems should I watch for?

Common problems: Error: TypeError: Cannot read properties of undefined — fixing the symptom with a null check instead of the root cause. Fix: trace the data flow to find where undefined originates.; Error: no preventive test added — "fix works but same bug regresses next refactor". Fix: add a regression test that reproduces the original error.; Error: trial-and-error debugging — "changed code until it worked without understanding why". Fix: require a root-cause explanation before any code change..

What are the best practices?

Recommended: Always trace back to the root cause before writing a fix — understanding precedes fixing.; Add a regression test that reproduces the original bug, then verify the fix makes it pass.; Document the root cause in the commit message so future developers understand the context..