TypeScript 5.2 Iteration Plan

[DanielRosenwasser]

This document outlines our focused tasks for TypeScript 5.2. 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
2023-05-30	TypeScript 5.1 Release
2023-06-23	Create 5.2 Beta (5.2.0) Build for Testing
2023-06-27	TypeScript 5.2 Beta Release
2023-08-04	Create 5.2 RC (5.2.1) Build for Testing
2023-08-08	TypeScript 5.2 RC Release
2023-08-18	Create 5.2 Final (5.2.2) Build for Testing
2023-08-22	TypeScript 5.2 Final Release 🚀

gantt
    dateFormat  YYYY-MM-DD
    TypeScript 5.1 Stabilization Period : 2023-05-15, 2023-05-30
    TypeScript 5.2 Beta Development : 2023-05-15, 2023-06-27
    TypeScript 5.2 RC Development : 2023-06-27, 2023-08-04
    TypeScript 5.2 Stabilization Period : 2023-08-04, 2023-08-22
todayMarker stroke-width:5px,stroke:#0f0,opacity:0.5

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Compiler and Language

• Decorator Metadata
• using Declarations
• Array method signature merging
• Investigate Type Argument Placeholders
• Investigate Plugins for File-Watching
• Investigate Custom Transformers in tsc
• Investigate Function Implementations Returning Indexed Access and Conditional Types
• Investigate Interop Across TypeScript and Bundlers for Default Imports
• lib.d.ts Updates

Editor and Language Service

• Refactor to Inline Variable
• Open-Ended String Completions
• Full Program Loads and ATA in vscode.dev
• Trailing Comma Completions for Object Members
• Completion Commit Characters
• Organize Imports Respecting type Imports
• Experiment with Better Names for Extracted Code
• Specify Node.js Executable for TSServer in VS Code
• Address Crawler-Detected Crashes

Performance

• Investigate Parallelized Parsing
• Investigate Caching Resolutions in .tsbuildinfo
• Share Path Resolution Between Projects When Possible
• Optimize JSDoc Parsing
• Track Narrowable Entities for Control Flow Analysis
• Deopt Explorer Upkeep

Website and Docs

• Author and Iterate on Module Documentation
• Website Build Speedup
• Scope and Infrastructure Website Changes
• Address Accessibility Issues

Infrastructure

• Use pnpm Workspaces in DefinitelyTyped
• Expand Performance Suite
• Performance Suite Infrastructure Setup

[DanielRosenwasser]

The previous Iteration Plan for TypeScript 5.1 is available here.

[fleddri]

Are there any plans or discussions regarding #53656?

[TmLev]

Also interested if you have any plans regarding #41316? Working on libraries seems impossible without it sometimes.

[Mike-Dax]

I've been recently hitting up against #53018 and #54029 seems to open a bunch of opportunities for reverse mapped types to receive better inference. It would be a real game changer to our main APIs. Is there anything a community member can do to help with something like this?

[max-kamps]

Is #14729 still being investigated? It got closed after #51328 got accepted for 5.1, but has since been re-opened since the PR didn't actually address most of #14729's usecases.

[DanielRosenwasser]

@typescript-bot sync release-5.2 and LKG

[typescript-bot]

Heya @DanielRosenwasser, I've started to sync release-5.2 with main for you. Here's the link to my best guess at the log.

[Andarist]

I've been recently hitting up against #53018 and #54029 seems to open a bunch of opportunities for reverse mapped types to receive better inference. It would be a real game changer to our main APIs. Is there anything a community member can do to help with something like this?

@Mike-Dax my PR isn't (yet) complete - it has some rough edges that I need to figure out. I'd happily collaborate on this one with somebody, I already know what I want to do there just need to find a proper way to fit those ideas into the code and the available data structures.

[fatcerberus]

Here's the link to my best guess at the log.

What the… what even kind of bot is this
Bad bot

[timbuckley]

Not explicitly mentioned above but this also lands support for Change Array By Copy methods (eg arr.toReversed(), arr.toSorted(), arr.with(index, value), etc).

Issue: #50333
PR: #51367
ECMAScript proposal: https://github.com/tc39/proposal-change-array-by-copy

[RyanCavanaugh]

FYI: #54923

[DanielRosenwasser]

@typescript-bot bump release-5.2

[typescript-bot]

Heya @DanielRosenwasser, I've started to update the version number on release-5.2 to 5.2.1-rc for you. Here's the link to my best guess at the log.

[eps1lon]

How template literals as computed properties on objects are now typed as literals instead of strings seems to not be mentioned in the changelog:

const key = 'foo'

// {
//    foo: number;
//    "foo-de": string;
// }

const object = {
    [key]: 1,
    [`${key}-de`]: "2"
}

// Errors in 5.1.6 with "Property 'match' does not exist on type 'string | number'."
object['foo-de'].match(/2/)
object['foo'] + 1;

Playground Link 5.2.0-beta

vs

const key = 'foo'

// {
//    [x: string]: string | number;
//    foo: number;
// }

const object = {
    [key]: 1,
    [`${key}-de`]: "2"
}


// @ts-expect-error
object['foo-de'].match(/2/)
object['foo'] + 1;

Playground Link 5.1.6

Seems like a good change but probably worth mentioning.

[Andarist]

If im not mistaken this was changed by #53907

[eps1lon]

Also positive change: referencing const enums in template literal types used to error under --isolatedModules but doesn't anymore:

export declare const enum OBJECT_INDICATION_TYPE {
    HIGHLIGHTED_DOT = "HIGHLIGHTED_DOT"
}
type Values<T> = {
    [K in keyof T]: T[K];
}[keyof T];
export type IndicationType = `${Values<typeof OBJECT_INDICATION_TYPE>}`;
// Fixed:                                     ^^^^^^^^^^^^^^^^^^^^^^ Cannot access ambient const enums when 'isolatedModules' is enabled.(274
export {};

Playground Link

[DanielRosenwasser]

@typescript-bot bump release-5.2

[typescript-bot]

Heya @DanielRosenwasser, I've started to update the version number on release-5.2 to 5.2.2 for you. Here's the link to my best guess at the log.

[dimatakoy]

Version 5.2.2 is already available on npm, but I don't see a corresponding tag and release/changelog in this repository. Can you add the actual release here on the github?

[DanielRosenwasser]

It's tagged now - but can I ask what you all use the tag for?

[timbuckley]

It's tagged now - but can I ask what you all use the tag for?

Speaking for myself: Github watch notifications on release tags to know when new releases happen.

[dimatakoy]

It's tagged now - but can I ask what you all use the tag for?

— Release notifications / changelogs
— Easy way to compare releases

[RHOOPH]

Not explicitly mentioned above but this also lands support for Change Array By Copy methods (eg arr.toReversed(), arr.toSorted(), arr.with(index, value), etc).

Issue: #50333 PR: #51367 ECMAScript proposal: https://github.com/tc39/proposal-change-array-by-copy

I've upgraded to 5.2.2 but still shows error.
Property 'toSpliced' does not exist on type 'string[]'. Did you mean 'splice'?
Am i missing something? @timbuckley

[timbuckley]

Not explicitly mentioned above but this also lands support for Change Array By Copy methods (eg arr.toReversed(), arr.toSorted(), arr.with(index, value), etc).
Issue: #50333 PR: #51367 ECMAScript proposal: https://github.com/tc39/proposal-change-array-by-copy

I've upgraded to 5.2.2 but still shows error. Property 'toSpliced' does not exist on type 'string[]'. Did you mean 'splice'? Am i missing something? @timbuckley

@RHOOPH I think your runtime (whether browser or Node) still needs to use toSpliced, independent of whether TypeScript understands that type (which it only does after 5.2).

Node v20 is the first Node version to support it, for example. Scroll down to that line in this compatibility chart: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array#browser_compatibility

[sacru2red]

target should set to esnext. In tsconfig.json