TypeScript v5.5

そのおかげでfilterで型推論がちゃんと効くようになった

code:ts

// birds: Bird[]

const birds = countries

.map(country => nationalBirds.get(country))

.filter(bird => bird !== undefined);

Control Flow Narrowing for Constant Indexed Accesses

code:ts

function f1(obj: Record<string, unknown>, key: string) {

// Now okay, previously was error

}

}

The JSDoc @import Tag

docs内で外部ファイルの型を参照する時に使う

Support for New ECMAScript Set Methods

WIP

Isolated Declarations

Consulting package.json Dependencies for Declaration File Generation

Editor and Watch-Mode Reliability Improvements

Performance and Size Optimizations

Easier API Consumption from ECMAScript Modules

The transpileDeclaration API

Notable Behavioral Changes

Disabling Features Deprecated in TypeScript 5.0

lib.d.ts Changes

Stricter Parsing for Decorators

undefined is No Longer a Definable Type Name

Simplified Reference Directive Declaration Emit

TypeScript 5.5 で tsconfig.json>module よりも package.json>type と拡張子を優先するようになったので、dualパッケージ生成ロジックが壊れた /

これどの話だ