Microsoft releases TypeScript 6.0, the last version built on JavaScript

Microsoft has just released TypeScript 6.0, a programming language built on JavaScript that allows developers to add type-checking to their JavaScript code. You can install it, or update the current version running on your computer, by running the following npm command:

• npm install -D typescript

The most notable thing about TypeScript 6.0 is that it's going to be the last release based on the current JavaScript compiler codebase. Microsoft is already working on TypeScript 7.0, and it will be a full rewrite in Go. According to Microsoft, switching the codebase should make programming in TypeScript 10 times faster.

As a transition release, 6.0 is mostly focused on cleanups and preparing developers for the move to 7.0. Still, there are new features, as well as a decent number of breaking changes in this release. Here's the full list of what's new and what changed in TypeScript 6.0:

• Less Context-Sensitivity on this-less Functions
• Subpath Imports Starting with #/
• Combining --moduleResolution bundler with --module commonjs
• The --stableTypeOrdering Flag
• es2025 option for target and lib
• New Types for Temporal
• New Types for getOrInsert Methods
• RegExp.escape
• dom lib now includes dom.iterable and dom.asynciterable
• strict now defaults to true
• types now defaults to []
• module defaults to esnext, target defaults to es2025
• Deprecated: target: es5, --outFile, --baseUrl, --moduleResolution node, --moduleResolution classic, AMD/UMD/SystemJS module targets

Microsoft also notified developers that many projects will need at least two immediate changes after upgrading to TypeScript 6.0. The first is explicitly setting "types": ["node"] in tsconfig, as the new empty default will cause a flood of missing identifier errors. The second is setting "rootDir": "./src" if it was previously being inferred automatically, otherwise, output files will end up in the wrong directory.

Microsoft says that the team is now entirely focused on developing TypeScript 7.0. The new TypeScript version is already available in native preview, and if you want to try it, you can do so by running the following command:

• npm install -D @typescript/native-preview

Microsoft is expected to release the stable version of TypeScript 7.0 in a few months.