TypeScript 4.0 Iteration Plan

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](https://github.com/microsoft/TypeScript/issues/37255)
* [Labeled Tuple Elements](https://github.com/Microsoft/TypeScript/issues/28259)
* [Class Property Inference from Constructors](https://github.com/microsoft/TypeScript/pull/37920)
* [Forward Declarations](https://github.com/microsoft/TypeScript/issues/31894)
* [Investigate the `awaited` Type](https://github.com/microsoft/TypeScript/issues/27711)
* [JSX Factory Updates](https://github.com/microsoft/TypeScript/issues/34547)
* [`unknown` on `catch` Clause Bindings](https://github.com/microsoft/TypeScript/issues/36775)
* [Variadic Tuples](https://github.com/microsoft/TypeScript/issues/5453)

## Editor Productivity

* Refactorings
    * [Convert to Optional Chaining and Coalescing](https://github.com/microsoft/TypeScript/issues/35018)
* [Discoverability in Refactoring](https://github.com/microsoft/TypeScript/issues/34930) ([ideas](https://github.com/microsoft/TypeScript/issues/37895))
* [Lightweight Navigation](https://github.com/microsoft/TypeScript/issues/37713)
* [Improved Auto-Import](https://github.com/microsoft/TypeScript/issues/37812)
* [Editor support for `/** @deprecated */` tags](https://github.com/microsoft/TypeScript/issues/390)
* [Editor support for `/** @see */` tags](https://github.com/microsoft/TypeScript/issues/35524)
* [Semantic Highlighting](https://github.com/microsoft/TypeScript/issues/38435)

## Performance

* More Type-Checking Optimizations
* Investigate Bottlenecks in Larger Apps

## Infrastructure

* [Migrate TypeScript to Modules](https://github.com/microsoft/TypeScript/pull/35561)
* Expand Commands Tested in TSServer Crawler
* GitHub Crawler Infrastructure to Find Breaking Changes

## Investigate High-Demand Bug Fixes

* [Don't Widen Computed Property Keys](https://github.com/microsoft/TypeScript/issues/13948)
* [Cleaning Files Under `--watch`](https://github.com/microsoft/TypeScript/issues/16057)
* [Higher Order Component Issues](https://github.com/microsoft/TypeScript/issues/28938)
* [Remove `--declaration` Emit Error](https://github.com/microsoft/TypeScript/issues/17293)
* [Inference for Proxies](https://github.com/microsoft/TypeScript/issues/20846)
* [`change` events on `<input type="file">`have no `files` field](https://github.com/microsoft/TypeScript/issues/31816)
* [Poor Error for `isolatedModules`](https://github.com/microsoft/TypeScript/issues/15230) 


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TypeScript 4.0 Iteration Plan #38510

DanielRosenwasser
openedon May 12, 2020

Language Features

Editor Productivity

Performance

Infrastructure

Investigate High-Demand Bug Fixes

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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 🚀