is-kit

Practical Guides

Start with a real TypeScript problem. Each guide explains the tradeoffs, builds a focused solution, and links to the relevant API reference.

Filter null and undefined from arrays in TypeScript
Remove nullish array entries without losing TypeScript narrowing or valid falsy values.
Keep hand-written type guards in sync with TypeScript types
Make missing, extra, and incompatible string-keyed guard fields visible when an existing object type changes.
Validate unknown without a schema library
Validate untrusted TypeScript values with small composable guards and a lightweight tagged result.