Dr. Axel Rauschmayer • 6/21/2025

TypeScript: checking Map keys and Array indices

This article details a common TypeScript issue where checking for a Map key with `.has()` doesn't refine the type from `undefined | V` to `V` when using `.get()`. It presents solutions including the non-null assertion operator, an alternative pattern, and a type guard augmentation for the Map interface to enable proper type narrowing.

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#TypeScript #type checking #array