What's New

When you follow an older tutorial or upgrade a project, check which release introduced a feature:

TypeScript releases from 5.0 to 7.0 (source: official release announcements)
Version	Released	Highlights
5.0	Mar 2023	Standard decorators, const type parameters, bundler mode
5.1	Jun 2023	Unrelated getter and setter types
5.2	Aug 2023	using declarations, decorator metadata
5.3	Nov 2023	Import attributes, switch (true) narrowing
5.4	Mar 2024	NoInfer<T>, narrowing preserved in closures
5.5	Jun 2024	Inferred type predicates, isolatedDeclarations
5.6	Sep 2024	Errors on always-truthy checks, iterator helpers
5.7	Nov 2024	Never-initialized variable checks
5.8	Feb 2025	erasableSyntaxOnly, require() of ESM in nodenext
5.9	Aug 2025	import defer, minimal tsc --init
6.0	Mar 2026	Last JavaScript-based release; new defaults
7.0	Jul 2026	Native Go compiler (TypeScript 6 and 7)

Three of these features in one file, checked by tsc 7.0 and run by Node.js 25 2,131 :

using (5.2), NoInfer (5.4) and inferred type predicates (5.5)JavaScript

function openLog(name: string) {
  console.log(`open ${name}`);
  return { [Symbol.dispose]: () => console.log(`close ${name}`) };
}
const pick = <T extends string>(options: T[], fallback: NoInfer<T>): T => options[0] ?? fallback;
{
  using log = openLog("audit");                                 // disposed at block end
  const ids = [3, undefined, 7].filter((id) => id !== undefined); // number[]
  console.log(ids.map((id) => id * 2), pick(["sm", "lg"], "sm"));
  pick(["sm", "lg"], "xl");
}

Output

$ npx tsc --noEmit
whatsnew.ts(10,22): error TS2345: Argument of type '"xl"' is not assignable to parameter of
  type '"lg" | "sm"'.
$ node whatsnew.ts
open audit
[ 6, 14 ] sm
close audit

Without NoInfer, T widens to include "xl" and the typo passes. TypeScript 5.4 also reports 'id' is possibly 'undefined': before 5.5 you had to write (id): id is number => ... yourself.

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