## Lesson — Validate numeric input before parseInt

**Tags:** typescript, validation

When accepting user input that should be a pure integer (CLI args, PR numbers), validate with `String(Number(val)) === val` or `/^\d+$/` before calling `parseInt`. The `parseInt` function silently accepts trailing non-numeric characters (e.g., `parseInt("123abc")` returns `123`). This is a code review guideline, not a lint-time pattern — `parseInt` itself is a valid function.
