TypeScript 5.0 Released: Decorators and const Type Parameters

What happened

TypeScript 5.0 was released on March 16, 2023, as announced on Microsoft's TypeScript blog. Despite the major version number, the team described it as a non-disruptive release, aiming to make TypeScript smaller, simpler and faster while adding significant new features, chief among them support for the standardised decorators proposal.

Decorators

TypeScript 5.0 implemented the ECMAScript decorators standard, a way to customise classes and their members in a reusable manner. Decorators let developers wrap a method or class with additional behaviour, for example logging entry and exit, or binding a method to its instance, using a concise @decorator syntax. Unlike TypeScript's older experimental decorators, this implementation followed the standard being developed by TC39, the JavaScript standards body.

const type parameters

The release added const type parameters, which let library authors ask TypeScript to infer the most specific, literal type for a generic argument rather than a widened one. This gives library authors more control over inference and produces more precise types for callers, without requiring the caller to add const assertions everywhere.

Better ESM and simpler configuration

TypeScript 5.0 improved support for ECMAScript modules in Node and bundlers, added a bundler module-resolution mode, and introduced flags such as verbatimModuleSyntax to give clearer control over how imports are emitted. It also simplified configuration by allowing multiple configuration files in extends, and expanded JSDoc support with tags like @satisfies and @overload.

Why it mattered

TypeScript 5.0 brought decorators in line with the emerging JavaScript standard, which mattered for frameworks and libraries that rely on them heavily. Combined with more precise generics, better ESM handling and a smaller, faster compiler, it kept TypeScript aligned with the direction of JavaScript while improving day-to-day performance, and the team emphasised that most developers would have an upgrade experience similar to previous releases.

Related on Skillo

See also: TypeScript 5.4's NoInfer and narrowing improvements.

Sources

• Announcing TypeScript 5.0 (official Microsoft blog)

Published date reflects the original event date (2023-03-16). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.