Introduction
Some mistakes show up again and again: off-by-one errors, ignoring failures, or copying code without understanding it. We'll list frequent ones and how to avoid them. A short checklist (did I handle errors? did I check bounds? did I name this clearly?) catches many issues before they reach production or code review. Same mistakes, same fixes—here are practical habits to prevent them.
What Is Common Coding Mistakes
Common coding mistakes are patterns that lead to bugs or maintenance pain: wrong assumptions (e.g. “this is never null”), unclear naming, duplicated logic, or not handling errors. They’re “common” because they’re easy to make under time pressure or when the problem isn’t fully specified. Recognizing them helps you catch your own and review others’ code better.
Why It Matters
Repeating the same kind of mistake costs time and erodes confidence. A short checklist (did I handle errors? did I check bounds? did I name this clearly?) catches many issues before they reach production or review.
How to Calculate It
Real-Life Example
You loop over an array to build a list. You use indices 1..length instead of 0..length-1 and miss the first element, or you use <= length and read past the end. Fix: use the language’s iterator (for (const x of arr)) or correct bounds (i < arr.length). Another: you call an API and only handle success; when the API is down, the app shows nothing or crashes. Fix: handle errors and show a message or fallback.
Common Mistakes
Assuming input is never null or empty. Ignoring return values or errors. Off-by-one in loops or array access. Copy-pasting and leaving the old variable or logic. Using == instead of === (or equivalent) and getting type coercion. Not validating or sanitizing user input. Hardcoding values that should be config. Writing a huge function instead of splitting it.
Practical Tips
- Validate inputs and handle “empty” and “error” paths explicitly.
- Use iterators or bounds you’re sure about; double-check loop conditions.
- Don’t ignore errors; log or handle them and fail clearly when appropriate.
- After copy-paste, search for the old name or literal and fix it.
- Run the code (or a test) with a minimal example and an error case.
FAQs
Conclusion
Many bugs come from the same patterns: unhandled errors, wrong bounds, unclear names, and copy-paste. Validate input, handle errors, check loop bounds, and review before you push. A small checklist goes a long way.