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docs: keep banner height in sync via ResizeObserver #9330

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Merged
jdx merged 1 commit into from
Apr 23, 2026
Merged

docs: keep banner height in sync via ResizeObserver #9330

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21 changes: 15 additions & 6 deletions docs/.vitepress/theme/banner.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -51,23 +51,32 @@ function render(b: BannerData): void {
el.appendChild(a);
}

const syncHeight = () => {
document.documentElement.style.setProperty(
"--vp-layout-top-height",
`${el.offsetHeight}px`,
);
};
Comment on lines +54 to +59

@gemini-code-assist gemini-code-assist Bot Apr 23, 2026

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medium

There is a potential race condition here. If the banner is dismissed (via the button click) before the requestAnimationFrame or a ResizeObserver notification fires, syncHeight will execute on a detached element. This will result in el.offsetHeight being 0, which then re-adds the --vp-layout-top-height property to the document as 0px after it was explicitly removed in the click handler. Adding a check for el.isConnected ensures the property is only updated if the banner is still active in the DOM.

Suggested change
const syncHeight = () => {
document.documentElement.style.setProperty(
"--vp-layout-top-height",
`${el.offsetHeight}px`,
);
};
const syncHeight = () => {
if (!el.isConnected) return;
document.documentElement.style.setProperty(
"--vp-layout-top-height",
`${el.offsetHeight}px`,
);
};


const observer =
typeof ResizeObserver !== "undefined"
? new ResizeObserver(syncHeight)
: null;

const btn = document.createElement("button");
btn.type = "button";
btn.setAttribute("aria-label", "Dismiss");
btn.textContent = "\u00d7";
btn.addEventListener("click", () => {
localStorage.setItem(STORAGE_KEY, b.id);
observer?.disconnect();
el.remove();
document.documentElement.style.removeProperty("--vp-layout-top-height");
});
el.appendChild(btn);

document.body.prepend(el);

requestAnimationFrame(() => {
document.documentElement.style.setProperty(
"--vp-layout-top-height",
`${el.offsetHeight}px`,
);
});
requestAnimationFrame(syncHeight);
observer?.observe(el);
}
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