Use a Distinct Type for Special Values

Overview

Don't use -1, 0, or "" as special values. Use null or a distinct type.

When a function can fail or have a special case, represent it with a type that TypeScript can distinguish, not an in-domain value like -1 that's just a regular number.

When to Use This Skill

• Functions that can fail (not found, error, etc.)
• Values that have a "missing" or "unknown" state
• Wrapping APIs that use sentinel values like -1
• Designing your own return types

The Iron Rule