iterate-objects-safely

SKILL.md

Iterating over objects in TypeScript is surprisingly tricky. The for...in loop infers keys as string rather than the object's keys, leading to indexing errors. This happens because objects can have additional properties beyond their declared type (structural typing), and for...in includes inherited properties.

Understanding safe iteration patterns helps you avoid any types and type assertions while correctly handling object traversal.

Use Object.entries for safe iteration over any object. Use for...in with keyof assertions only when you know the exact shape. Consider Map for guaranteed type safety.

Use when iterating over object keys and values. Use when for...in loops produce type errors. Use when Object.entries returns any types. Use when dealing with prototype pollution concerns. Use when considering Map vs object. Source: marius-townhouse/effective-typescript-skills.

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