TypeScript 4.9 Support

[bradzacher]

https://devblogs.microsoft.com/typescript/announcing-typescript-4-9-rc/

This issue is just to track all of the new features and their implementation state in this project.
As with all releases, we will not necessarily to support all features until closer to the full release when everything the features are stabilised.

Please be patient.

✅ The satisfies Operator (#5717)

const palette = {
    red: [255, 0, 0],
    green: "#00ff00",
    bleu: [0, 0, 255]
//  ~~~~ The typo is now caught!
} satisfies Record<Colors, string | RGB>;

This will require AST changes

✅ Auto-Accessors in Classes (#5926)

class Person {
    accessor name: string;

    constructor(name: string) {
        this.name = name;
    }
}

This will require AST changes.
This feature is based on the stage-3 decorators proposal.
We will need to implement the defined ESTree AST

✅ substitute Replaced With constraint on SubstitutionTypes

We will need to double-check our codebase for usages of the old property.

✅ lib.d.ts Updates

We will need to regenerate our types within scope-manager.

---

Other changes with no impact to us

• Unlisted Property Narrowing with the in Operator
• Checks For Equality on NaN
• File-Watching Now Uses File System Events
• "Remove Unused Imports" and "Sort Imports" Commands for Editors
• Go-to-Definition on return Keywords
• Performance Improvements
• Breaking Changes
  • Better Types for Promise.resolve
  • JavaScript Emit No Longer Elides Imports
  • exports is Prioritized Over typesVersions

[JoshuaKGoldberg]

will it only be released once auto-accessor support is added?

You can always use our canary versions: https://github.com/typescript-eslint/typescript-eslint/tree/a4f85b8cfe38ba8ea2a2ac4a56d9b11a81a8a15a#versioning.

We publish a canary release on every successful merge to main, so you never need to wait for a new stable version to make use of any updates.

Additionally, we promote to the latest tag on NPM once per week, on Mondays at 1 pm Eastern.

5.43.1-alpha.22 was released yesterday and does include support for satisfies.

I've also filed #6046 that we should document exactly how to use canary versions. See that issue's description for npm and yarn commands you can use.

---

Was this not released with @typescript-eslint v5.43.0

No, satisfies was merged in #5717 on November 17th. 5.43.0 was released November 14th: https://github.com/typescript-eslint/typescript-eslint/releases/tag/v5.43.0.

---

We're blocked on fully supporting TypeScript 4.9 on #5926, which is waiting for a decision on naming alignment discussion with ESTree (estree/estree#292).

I'm going to lock this thread because there's nothing to discuss until #5926 lands. Thanks for your interest everyone - hopefully it'll be soon!

[bradzacher]

accessor support has merged and will be released as part of the standard cycle!

so next release will officially have full support for TS 4.9, closing.