TypeScript 5.6 Features Every Developer Should Use in 2026

TypeScript 5.6 Features Every Developer Should Use in 2026

TypeScript 5.6 adds features that improve both developer experience and type safety. These are the ones that matter for everyday coding.

NoInfer Utility Type

Prevent TypeScript from widening generic types in positions where you want the user to be explicit:

function createFSM<S extends string>(
  initial: S,
  transitions: Record<S, NoInfer<S>[]>
) { ... }

// Now TypeScript errors if transitions reference unlisted states
createFSM("idle", {
  idle: ["loading"],
  loading: ["success", "error"],
  success: ["idle"],
  error: ["idle", "retry"]  // Error: "retry" not in S
});

Isolated Declarations

Generate .d.ts files without type-checking the entire project. Build times for large monorepos drop significantly because declaration emit can be parallelized across packages.

Import Attributes

import config from "./config.json" with { type: "json" };
import styles from "./app.css" with { type: "css" };

Explicit import types replace the fragile "guess from file extension" behavior. Bundlers and runtimes can optimize based on declared types.