TypeScript 5.0 features

[nicolo-ribaudo]

• const type parameters - https://devblogs.microsoft.com/typescript/announcing-typescript-5-0-beta/#const-type-parameters ([ts] Support const modifier in type parameters #15384)
• export type * from - https://devblogs.microsoft.com/typescript/announcing-typescript-5-0-beta/#support-for-export-type ([ts] Support export type * from #15381)
  • I remember I needed to use this somewhere in our code, but I cannot find where anymore

[JLHwung]

Although TS 5.0 also supports ES decorators, we will not add decorators transform to the preset-typescript like we did for other stage 3 features. Use the following config if you want to try ES decorators and TS 5.0 features:

{
  "presets": ["@babel/preset-typescript"],
  "plugins": [["@babel/plugin-proposal-decorators", { "version": "2022-03" }]]
}

[liuxingbaoyu]

babel
ts

There is a possible output optimization(const enum) here, but it's not urgent, we can implement it when we have time.

microsoft/TypeScript#50528

Fixed in #15379

[JLHwung]

I remember I needed to use this somewhere in our code, but I cannot find where anymore

@nicolo-ribaudo Did you mean

babel/packages/babel-types/src/index.ts

Line 104 in 90ad7e9

export * from "./ast-types/generated";

?

[nicolo-ribaudo]

Yes!

[nicolo-ribaudo]

The TS decorators syntax is slightly different from the JS decorators syntax: tc39/proposal-decorators#69

However, since there is active discussion about it, I prefer to wait until TS 5.0 stable before implementing it.

[wycats]

Although TS 5.0 also supports ES decorators, we will not add decorators transform to the preset-typescript like we did for other stage 3 features. Use the following config if you want to try ES decorators and TS 5.0 features:

{
  "presets": ["@babel/preset-typescript"],
  "plugins": [["@babel/plugin-proposal-decorators", { "version": "2022-03" }]]
}

What's the rationale?

[JLHwung]

preset-typescript only transforms TS-only language features. Decorators, as an ES language feature, will be included in preset-env eventually when it reaches stage 4.

[nicolo-ribaudo]

For example, @babel/preset-typescript doesn't transform class fields even if TSC does.

[nicolo-ribaudo]

Released in 7.21.0