Inconsistent types between Document scrollingElement and documentElement

[aayla-secura]

🔎 Search Terms

I think document.scrollingElement should be of type Document["documentElement"] | null instead of Element | null. The spec (e.g. this and this) says that in standards mode scrollingElement returns the document root, which is document.documentElement and in quirks mode returns document.body or null.

document.body is always HTMLElement (right?) In principle, document.documentElement does not have to be HTMLElement (and there's an open issue about this, #29052, but currently Document.documentElement is still defined as HTMLElement, for some reason. So how come document.scrollingElement is not HTMLElement | null?

🕗 Version & Regression Information

N/A

⏯ Playground Link

No response

💻 Code

// Your code here

🙁 Actual behavior

document.scrollingElement is of type Element | null whereas document.documentElement and document.body are both of type HTMLElement.

🙂 Expected behavior

The non-null part of document.scrollingElement should be the same type as document.documentElement, which technically should be Element, but if document.documentElement is left as HTMLElement, as is currently, then document.scrollingElement should also be this.

Additional information about the issue

No response

[RyanCavanaugh]

Document.documentElement and Document.body are declared as HTMLElement, but Document.scrollingElement is still declared as Element | null. This produces TS2322 in TypeScript 6.0.3 and current native TypeScript 7.1.0-dev.20260918.1 when assigning it to HTMLElement | null.

A standards-mode browser document returned its HTMLHtmlElement document root from document.scrollingElement.

// Expected: document.scrollingElement is assignable to HTMLElement | null.
// Actual: it is declared Element | null, producing TS2322.
const element: HTMLElement | null = document.scrollingElement;