TypeScript 6.0 Beta: What the upgrade really means for everyday project
The beta is now on npm, so developers can try it with npm install -D typescript@beta. This article shows which new defaults will bite you, which deprecations demand a quick fix, and whether the shiny Temporal types are worth the hassle right now.
Why the “beta” label matter
The release is a bridge to the upcoming native Go‑based compiler in 7.0, not just another feature dump. In practice that means many knobs have been turned toward future‑proofing, and some of those knobs already change observable behavior. A team at a mid‑size SaaS company noticed their generated declaration files flipping the order of union members after adding an unrelated const at the top of a module—exactly the kind of nondeterminism the new --stableTypeOrdering flag tries to tame.
Getting the beta into a project without breaking everything
First, install the package as a dev dependency. Then run npx tsc --init if there is no existing config; otherwise open the current tsconfig.json. The most visible changes are default values that now assume an evergreen world:
- strict defaults to true – projects that never turned it on will start seeing “missing property” errors. Adding explicit type annotations where they were previously omitted usually resolves those.
- module now defaults to esnext – any code still emitting CommonJS will need either a manual "module": "commonjs" override or a migration plan toward ESM.
- target points at the latest ECMAScript version (currently es2025). If the build pipeline includes older browsers, pin the target back to an earlier year.
After adjusting those three settings, run the compiler. The first pass will likely surface missing global types because the new default for types is an empty array. Adding "types": ["node"] (or whatever globals are required) clears the cascade of “cannot find name” errors.
Finally, if the project still references any deprecated flags—--downlevelIteration, amd, umd, or systemjs modules—the compiler will emit a deprecation error and stop. The fix is simply to drop those options; modern bundlers handle the same scenarios far more efficiently.
Breaking changes that actually bite
The most common source of surprise is the removal of target: es5. A handful of legacy libraries still ship ES5‑only bundles, and trying to compile them with the default target will now produce syntax errors. The recommended workaround is to feed those files through a separate transpilation step (for example, Babel) before TypeScript sees them.
Another subtle change concerns baseUrl. Historically it acted as a catch‑all for module resolution, often masking path‑mapping mistakes. With its deprecation, any import that relied on an implicit lookup will now fail loudly. The fix is to convert the old "baseUrl": "./src" into explicit prefixes inside the paths map.
The outFile option has vanished entirely. Projects that used it to concatenate output for a simple script should switch to a bundler like esbuild or Vite; those tools not only respect TypeScript’s type information but also produce smaller, faster bundles.
New features worth playing with
- Temporal types – The API is already usable in Node 20 and modern browsers behind flags. Adding "lib": ["esnext", "dom"] (or the more granular temporal.esnext) enables full IntelliSense for Temporal.PlainDate, Instant, etc. Early adopters can experiment without any runtime penalty, but production code should still guard against environments that haven’t shipped the proposal.
- Subpath imports with “#/” – Node 20 now permits import foo from "#/utils" when the package’s package.json defines "imports": { "#/*": "./dist/*" }. TypeScript 6.0 mirrors this under the node20, nodenext, and bundler module‑resolution modes, so developers can finally retire long relative paths like ../../../utils.
- Stable type ordering – Enabling --stableTypeOrdering makes the beta’s output match what 7.0 will produce, eliminating noisy diffs in CI pipelines that compare declaration files across versions.
When to skip the beta entirely
If a codebase is locked behind an older bundler that still expects CommonJS output, or if the team relies on a custom outFile concatenation script, staying on 5.9 until those tools are upgraded is sensible. The beta also brings a noticeable compile‑time slowdown when --stableTypeOrdering is turned on—up to a quarter slower in large monorepos. For day‑to‑day development that matters, keeping the flag off and accepting nondeterministic .d.ts ordering may be the lesser evil.
Conversely, any project already using strict mode, ES2020+ targets, and ESM modules will find the migration almost painless. The real benefit is future‑proofing: once 7.0 lands, the jump from 6.0 will be mostly about the native Go compiler speed boost rather than another round of breaking changes.
Bottom line
The TypeScript 6.0 beta isn’t just a preview; it’s a litmus test for how ready a project is for the next wave of performance and language features. If the upgrade path feels like a series of tiny, predictable edits—add a types array, flip a couple defaults, drop deprecated flags—the codebase will likely reap the stability gains without much friction. If those steps look like a mountain, waiting for a more polished release or sticking with 5.9 is perfectly reasonable.
For more information and a detailed change log, visit the official release announcement below:
Announcing TypeScript 6.0 Beta
Today we are announcing the beta release of TypeScript 6.0! To get started using the beta, you can get it through npm with the following command: npm install -D typescript@beta TypeScript 6.0 is a unique release in that we intend for it to be the last release based on the current JavaScript codebase.
