Avoid Numeric Index Signatures

Overview

JavaScript object keys are always strings, even for arrays.

TypeScript's numeric index signatures are a helpful fiction for catching mistakes, but they don't reflect JavaScript's runtime behavior. Use Array, tuple, or ArrayLike types instead.

When to Use This Skill

• Defining array-like types
• Understanding JavaScript's array behavior
• Choosing between arrays and objects
• Working with Object.keys on arrays

The Iron Rule