Dr. Axel Rauschmayer • 6/21/2025

TypeScript: checking Map keys and Array indices

Read Original

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.

0 comments
#TypeScript #type checking #array
TypeScript: checking Map keys and Array indices

Comments

No comments yet

Be the first to share your thoughts!

Browser Extension

Get instant access to AllDevBlogs from your browser

Top of the Week

1
React vs Browser APIs (Mental Model)
Jivbcoop • 3 votes
2
React, useEffect, and Stale Closures: How to Avoid Them with Dependencies and useRef
Jivbcoop • 2 votes
3
Building Type-Safe Compound Components
TkDodo Dominik Dorfmeister • 2 votes
4
Using Browser Apis In React Practical Guide
Jivbcoop • 1 votes
5
Better react-hook-form Smart Form Components
Maarten Hus • 1 votes