TypeScript 5.5 Iteration Plan

[DanielRosenwasser]

This document outlines our focused tasks for TypeScript 5.5. It minimally indicates intent to investigate tasks or contribute to an implementation. Nothing is set in stone, but we will strive to complete these tasks in a reasonable timeframe.

Date	Event
2024-03-05	TypeScript 5.4 Release
2024-04-19	Create 5.5 Beta (5.5.0) Build for Testing
2024-04-24	TypeScript 5.5 Beta Release
2024-05-31	Create 5.5 RC (5.5.1) Build for Testing
2024-06-04	TypeScript 5.5 RC Release
2024-06-14	Create 5.5 Final (5.5.2) Build for Testing
2024-06-18	TypeScript 5.5 Final Release 🚀

gantt
    dateFormat  YYYY-MM-DD
    TypeScript 5.4 Stabilization Period : 2024-02-16, 2024-03-05
    TypeScript 5.5 Beta Development : 2024-02-16, 2024-04-19
    TypeScript 5.5 RC Development : 2024-04-20, 2024-05-31
    TypeScript 5.5 Stabilization Period : 2024-06-01, 2024-06-18
todayMarker stroke-width:5px,stroke:#0f0,opacity:0.5

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Compiler and Language

• The --isolatedDeclarations Flag
• Type-Only Imports in JSDoc
• Non-Null Assertions in JSDoc
• Regex Syntax Validation
• Checks for Never-Initialized Variables
• Allow Implementing Functions That Return Conditional Types
• Improvements in Extending tsconfig.json Files
• Investigate Recursive Object Type References
• Investigate Speculation Infrastructure for Overload Resolution
• Provide Better default Import Interop Configurability
• Improve default Import Detection from ECMAScript Modules
• ECMAScript Set Methods
• lib.d.ts Updates
• Removal of 5.0-Deprecated Functionality in 5.5

Editor and Language Service

• Auto-Import on Paste
• Region-Prioritized Error Checking
• Investigate AI-powered Refactorings
• Provide Code Action Ranges
• TSServer File-Watching Events
• Improve Organize Import Ordering
• Investigate Simpler Quick Fix API
• Define Initial Sketch of LSP Support

Performance

• More Caching in --incremental Mode
• Improved Performance for Git Branch Switching Scenarios
• Investigate Running With V8 Snapshots

Website and Docs

• Simplify and Refactor Website for Faster Builds

Infrastructure

• Adopt --isolatedDeclarations and Parallelize TypeScript's Build

[DanielRosenwasser]

The previous iteration plan is available here.

[kevinbarabash]

How much of an impact will --isolatedDeclarations have on type checking performance in large projects?

[jakebailey]

None directly, in the same way that isolatedModules doesn't speed things up in and of itself.

But, if you have code which passes isolatedModules, it can be safely transpiled by an external tool (like Babel, esbuild, swc). And similarly, code passing isolatedDeclarations can be transpiled into a declaration file by an external tool too (once one exists).

[jakebailey]

(This isn't to say that there can't be some speedups possible in TypeScript in the future enabled by this option, just that the flag itself is intended to just be checks.)

[JVKdouk]

Hey everyone, any chance of getting #26242 in this release? It was proposed back in 2018 and there has not been much work on the issue up to this point. Getting it at least planned would already be amazing to the TS community. I believe it would substantially improve the power of TS in the long run!

[clearfram3]

Just a heads up, I'm working on remaking the website using Sveltekit. Styles will be the same, but the overall structure will be simpler and much quicker to iterate on.

[DanielRosenwasser]

@ClearedFram3 while I don't want to discourage experimentation, I don't think we would accept such a large PR without discussing changes ahead of time.

[clearfram3]

@DanielRosenwasser I should've said the codebase structure will be different—the website style/content structure will be the same. After the current codebase is replaced, there will ample room for discussion about changing design and content or even to a different framework haha.

[graphemecluster]

I’ve been watching the iteration plan threads from 5.4 seeing my PR (#55600) on the list. I am on standby anytime for any necessary alternations.

[jwalkerinterpres]

Is there anything Typescript community members can do to influence this list?

I think I can speak for every TS React dev on the planet when I say that #29526 (improved syntax for destructuring an argument ... like the React props argument) has languished long enough. The community has essentially reached a consensus on a desired syntax in that ticket (something that was not easy), and now all that's needed is developer will to implement.

I can't speak for anyone else, but personally I would trade everything on the 5.5 list for this one feature!

[aspirisen]

A question about Investigate Recursive Object Type References
Will it help i.e. in zustand in avoiding writing interface for the state, and instead just infer the type from the initial state (create-function argument)?

[jcalz]

• Allow Implementing Functions That Return Conditional Types

Cross-linking #33912 and #56941