TypeScript 5.9 Iteration Plan

[DanielRosenwasser]

Date	Event
2024-02-25	TypeScript 5.8 Release
2024-05-23	Create 5.9 Beta (5.9.0) Build for Testing
2024-05-26	TypeScript 5.9 Beta Release
2024-06-13	Create 5.9 RC (5.9.1) Build for Testing
2024-06-17	TypeScript 5.9 RC Release
2024-07-18	Create 5.9 Final (5.9.2) Build for Testing
2024-07-22	TypeScript 5.9 Final Release 🚀

Compiler and Language

• tsc --init Updates
• 6.0 Deprecation Plans
• Investigate Cyclic Project References
• node20 Resolution
• lib.d.ts Updates

Editor and Language Service

• Expandable Hovers

Performance

• Port to Native
• Cache Mapper Instantiations

[controversial]

Is the “Checked Returns for Conditional and Indexed Access Types” feature (originally #56941, now #61359) planned to re-land in 5.9?

(this feature was included in 5.8 beta, but reverted before the RC; @gabritto had mentioned the feature could re-land in 5.9)

[DanielRosenwasser]

We're not planning on bringing that in for 5.9. We want to be more conservative about larger features that are more involved while so much of our attention is currently on the port.

[controversial]

understood, thanks for clarifying @DanielRosenwasser

should we expect that that feature (or others of similar scope) won’t land in Typescript until 7.x?

i.e. should we expect it will never land in Strada—in order to avoid the additional development burden of trying to port a “moving target”—but instead the team will hold off until Corsa is ready to be the target of new features like this one?

(to be clear, that approach would not be at all unreasonable to me, just curious what to expect!)