Repository navigation
TypeScript 4.0 Iteration Plan #38510
Description
This document outlines our focused tasks for TypeScript 4.0, as well as some of the discussion that explains how/why we prioritized certain work items. Nothing is set in stone, but we will strive to complete them in a reasonable timeframe.
| Date | Event |
|---|---|
| May 12th | TypeScript 3.9 Release (past) |
| June 22nd | Create 4.0 Beta (4.0.0) Build for Testing |
| June 25th | TypeScript 4.0 Beta Release |
| July 31st | Create 4.0 RC (4.0.1) Build for Testing |
| August 6th | TypeScript 4.0 RC Release |
| August 14th | Create 4.0 Final (4.0.2) Build for Testing |
| August 20th | TypeScript 4.0 Final Release 🚀 |
Language Features
- Short-Circuiting Assignment Operators
- Labeled Tuple Elements
- Class Property Inference from Constructors
- Forward Declarations
- Investigate the
awaitedType - JSX Factory Updates
unknownoncatchClause Bindings- Variadic Tuples
Editor Productivity
- Refactorings
- Discoverability in Refactoring (ideas)
- Lightweight Navigation
- Improved Auto-Import
- Editor support for
/** @deprecated */tags - Editor support for
/** @see */tags - Semantic Highlighting
Performance
- More Type-Checking Optimizations
- Investigate Bottlenecks in Larger Apps
Infrastructure
- Migrate TypeScript to Modules
- Expand Commands Tested in TSServer Crawler
- GitHub Crawler Infrastructure to Find Breaking Changes
Activity
checkmatez commentedon May 13, 2020
Would you consider to include #29818 in 4.0 maybe behind experimental flag?
Jessidhia commentedon May 14, 2020
That gets complicated by the change in factory function definition in itself.
It could be interesting to introduce a separate factory virtual type definition, though; say,
JSX.Factory, orReact.JSX.Factory, which TypeScript could then use for inference. I'm not quite sure just translating JSX grammar to function calls is sufficient or efficient but, since it's a virtual type, it doesn't have to correspond to any concrete JavaScript entity. The risk, of course, is getting into the same situation as we have now, with a bunch of virtual types that ended up limiting the type safety, not only of children, but of several features introduced after React 15.ExE-Boss commentedon May 17, 2020
Would you consider to also include #24738 in 4.0 as well?
leemhenson commentedon May 18, 2020
I'm a bit sad to see no mention of #33038 [👍 140 and an actual PR by your own Wesley Wigham (@weswigham)] or #202 [👍 390] while tickets like #15230 [👍 27] are considered "high-demand". I realise you can't really compare or prioritise on the basis of "likes" but it would be great if there was some roadmap update on these, especially as 4.0 seems like nice opportunity to introduce a feature like this. 🙏
Skillz4Killz commentedon May 19, 2020
~3.5-year-old issue awaiting feedback with almost 200 comments #13778 with inaccurate typings provided for stuff like array destructuring. Pwetty pwease can we implement fix 🙏
DanielRosenwasser commentedon May 19, 2020
I appreciate people occasionally boosting issues that they believe need attention on the roadmaps and iteration plans, but I think I need to be clear here -that "investigate high demand bug fixes" section was determined by looking through issues that were clearly causing a lot of papercuts but which seemed reasonable in scope. We're definitely still mindful of the issues mentioned, but some of them are not as scoped nor do they have a clear ideal outcome.
Examples:
undefinedon index signatures is an example of something that's interesting, but we don't want to add behavior that makes it harder for 90% of people who already operate under the current assumptions. Finding an approach that composes and allows users to incrementally adopt those checks isn't something that's obvious to us. Even if it's technically possible with a bunch of conditional types and special compiler checks, those solutions tend to be very clearly hacky and break down fast.aminpaks commentedon May 20, 2020
Daniel Rosenwasser (@DanielRosenwasser) what is the future language direction in your vision?
DanielRosenwasser commentedon May 20, 2020
I guess I'll give some context on where my mind is with nominality. There are a lot of different ideas people have in mind when they ask about nominal types, including
structs in C/C++/C#,newtypein Haskell, inline classes in Kotlin)There are shades between some of these (e.g. placeholder type declarations - kind of variant of opaque types that fall back to an implementation type), and then there are different directions that blend each of these together.
Ryan Cavanaugh (@RyanCavanaugh) had a great analogy about this where 3 kids are asking their parents for a pet. One wants a dog, one wants a cat, one wants a fish. They ask their parents "when are we getting a pet!?" Clearly they all agree they want a pet, but each wants a different pet!
Do I like branded types? I do! Branded types achieves something like distinct aliases, and fits the bill for what most users are looking for. But I don't think that's the right way to think about it. There's more design space to be fleshed out with plenty of known tradeoffs, and nothing giving me a sense that we need to rush a solution ASAP.
ExE-Boss commentedon May 21, 2020
I’d like if we could get microsoft/TypeScript-DOM-lib-generator#858 into TypeScript 4.0.
benjamingr commentedon May 21, 2020
Daniel Rosenwasser (@DanielRosenwasser) first of all thank you for the writeup 🙇
Can you elaborate a bit on what use cases nominal types actually address for TypeScript?
First: feel free to send me to a giant wall of text or a repo and I'll read it :]
I don't mean opaque types like placeholder types - I mean what you call "Traditional" nominal types.
I always felt nominal types were antithetical to JavaScript and that's why previous attempts didn't really work so well. There are ways to make it work pretty nicely (protocols in swift and typeclasses in haskell come to mind as "Nominal but extendable from the outside") and I'm sure you're familiar with most of the "well established" ways (I assume "units of measure" is an F# wink).
I have found a lot of people asking for nominal (as in "traditional") types but not a lot of writeups about why.
DanielRosenwasser commentedon May 22, 2020
Over time, we've seen fewer and fewer people request "traditional" nominal types, maybe because collectively the community has built up a mental mode for structural types. There are some places where types truly do act nominally (when
instanceofis involved or when there are privates). Some of that is captured with better control flow analysis and compatibility checks, but it's not perfect.Some of the "traditional" use-cases are the same as those of a zero-overhead nominal wrapper type (e.g.
newtype), and a lot of the time the intent there is to ensure special handling for things like file paths, untrusted strings, etc.chyzwar commentedon May 24, 2020
I kind of feel that Typescript is already expressive enough. What I would personally would like to see is better tooling integration.
yarn-pnp#28289 Native support for PnP #35206Because of above it is common to see clunky and hacky solutions. Most react projects have babel included for react-hot-loader (compiler plugins), some CSS systems also require babel for compile time transforms. Using pnp, esm or even CSS modules require more tooling and workarounds for tsc limitations.
It is also frustrating that for some of these issues community came with concrete solutions in form of PRs or proposals but these were rejected or stalled for years. As a practitioner, it is getting harder to use TS in the context of wider ecosystem.
Anyway I am just random person from internet.
JoshuaKGoldberg commentedon May 27, 2020
Daniel Rosenwasser (@DanielRosenwasser) maybe #29374 could get reviewed in time for 4.0? I think it covers many (most?) of the
this-before-supercases folks tend to ask about.41 remaining items
Aravin commentedon Aug 20, 2020
it's Aug 20 :)
DanielRosenwasser commentedon Aug 20, 2020
Heh, it's still August 19th here, and even 20 minutes from now I think you'll have to wait a bit more. We have nightly releases on npm if you can't take another minute! 😄
Ayfri commentedon Aug 20, 2020
Waiting for the release, already out in npm :)
DanielRosenwasser commentedon Sep 18, 2020
TypeScript Bot (@typescript-bot) bump release-4.0
typescript-bot commentedon Sep 18, 2020
Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to update the version number on
release-4.0to4.0.3for you. Here's the link to my best guess at the log.DanielRosenwasser commentedon Oct 19, 2020
TypeScript Bot (@typescript-bot) bump release-4.1
typescript-bot commentedon Oct 19, 2020
Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to update the version number on
release-4.1to4.1.1-rcfor you. Here's the link to my best guess at the log.DanielRosenwasser commentedon Oct 19, 2020
Oh no
DanielRosenwasser commentedon Oct 19, 2020
TypeScript Bot (@typescript-bot) bump release-4.0
typescript-bot commentedon Oct 19, 2020
Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to update the version number on
release-4.0to4.0.4for you. Here's the link to my best guess at the log.DanielRosenwasser commentedon Oct 26, 2020
TypeScript Bot (@typescript-bot) bump release-4.0
typescript-bot commentedon Oct 26, 2020
Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to update the version number on
release-4.0to4.0.5for you. Here's the link to my best guess at the log.DanielRosenwasser commentedon Jun 16, 2021
TypeScript Bot (@typescript-bot) bump release-4.0
typescript-bot commentedon Jun 16, 2021
Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to update the version number on
release-4.0to4.0.8for you. Here's the link to my best guess at the log.