DOM: `Element#matches()` incorrectly narrows types

🔎 Search Terms

element matches narrow never

🕗 Version & Regression Information

• This changed between versions 5.9.3 and 6.0.3

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.3#code/CYUwxgNghgTiAEEQBd4iQWxAO2QLngAkAVAWQBkBRTHZAbgCgBCdELXAOgymTAAsQAZwAU8AOTBkY+AEp4AMnloanbrwEjxwYNJlA

💻 Code

declare let element: HTMLElement;
!element.matches( 'dt' ) && element.matches( 'dd' )

🙁 Actual behavior

element.matches( 'dd' ) throws a Property 'matches' does not exist on type 'never' compilation error.

🙂 Expected behavior

element.matches( 'dd' ) does not throw any error.

Additional information about the issue

element.matches( 'dt' ) uses the following overload:

matches<K extends keyof HTMLElementTagNameMap>(selectors: K): this is HTMLElementTagNameMap[K];

The return type of element.matches( 'dt' ) is then this is HTMLElementTagNameMap['dt'] that maps to this is HTMLElement.

Since this is HTMLElement:

• When false, the type of element is HTMLElement (not narrowed further).
• When false, the type of element is never.

リンクされた TypeScript Playground の例から始め、issue に示されている Element#matches のオーバーロードを調べ、否定チェックの後に型述語が HTMLElement をどのように絞り込むかを追跡します。2 回目の element.matches('dd') 呼び出しが、Property 'matches' does not exist on type 'never' エラーなしでコンパイルできれば、issue は完了です。