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TypeScript

TypeScript 6.0: The Last JavaScript-Based Release

TypeScript
JavaScript

Mar 25, 2026- Sergio Zabala

The End of an Era

On March 23, 2026, the TypeScript team shipped version 6.0, and with it closed a chapter that started back when the compiler was first written in JavaScript. According to the official announcement on the TypeScript devblog, 6.0 is explicitly “the last release based on the current JavaScript codebase.” Everything from here on, starting with TypeScript 7.0, will run on a compiler rewritten in Go, built to take advantage of native code speed and shared-memory multi-threading.

That framing matters more than any single feature in this release. TypeScript 6.0 isn’t just another yearly update: it’s a deliberate bridge, and the team says as much: “most changes in TypeScript 6.0 are meant to help align and prepare for adopting TypeScript 7.0.”

New Language Features

Temporal API support. The Stage 4 Temporal proposal is now part of TypeScript’s built-in types when you target esnext:

const yesterday = Temporal.Now.instant().subtract({ hours: 24 })

ES2025 as a target and lib option. You can now set "target": "es2025" or add "es2025" to lib, which brings in RegExp.escape(), Promise.try(), new iterator helpers, and additional Set methods.

Map/WeakMap “upsert” methods, available via the esnext lib:

const cache = new Map<string, number>()
cache.getOrInsert('hits', 0)
cache.getOrInsertComputed('misses', () => expensiveDefault())

Subpath imports starting with #/. Combined with nodenext or bundler resolution, you can now alias without extra path segments:

{ "imports": { "#/*": "./dist/*" } }

Checker Improvements

Inference around methods that don’t reference this got smarter: TypeScript now prioritizes those functions during type inference, fixing cases where generic type parameters failed to resolve when object properties were reordered (a fix contributed by Mateusz Burzyński).

There’s also a new --stableTypeOrdering flag. It aligns 6.0’s type ordering with the deterministic algorithm TypeScript 7.0 will use for parallel type checking. It can cost up to a 25% slowdown, so it’s meant as a migration diagnostic, not something you leave on permanently.

The dom library was also consolidated: dom.iterable and dom.asynciterable are folded in by default, so for (const el of document.querySelectorAll("div")) just works without extra config.

Deprecations and Breaking Changes

This is where the “bridge” framing becomes concrete. Several defaults changed:

  • strict: true (was false)
  • module: "esnext" (was "commonjs")
  • target now floats to the current-year ES version (es2025 today)
  • types: [] by default, instead of auto-discovering everything under @types
  • noUncheckedSideEffectImports: true, libReplacement: false
  • rootDir now defaults to the tsconfig.json directory

And a long list of legacy options got deprecated or removed outright: target: es5 (ES2015 is now the floor), --downlevelIteration, --moduleResolution node (node10, in favor of nodenext/bundler), --module amd|umd|systemjs|none, --baseUrl (fold the prefix into paths instead), --moduleResolution classic, --esModuleInterop false, --allowSyntheticDefaultImports false, --alwaysStrict false, --outFile, the legacy module keyword for namespaces (use namespace), the asserts keyword on imports (use with), and the no-default-lib triple-slash directive.

Command-line file arguments alongside an existing tsconfig.json now error by default too, unless you pass --ignoreConfig.

Every one of these removes a pattern the native Go compiler either won’t support or wants to standardize away before it lands.

Conclusion: A Necessary Evolution

TypeScript 6.0 isn’t chasing flashy new syntax: it’s cleaning house. Stricter defaults, dropped legacy options, and a diagnostic flag for the checker’s future ordering algorithm all point the same direction: getting the ecosystem ready for a compiler that, according to the TypeScript team, is “extremely close to completion” and already previewable through the @typescript/native-preview package. If your project still leans on commonjs modules, loose strict settings, or node10 resolution, 6.0 is your cue to migrate now, while the transition is still gradual, because 7.0 won’t be carrying that baggage forward.