Fix mermaid diagram height when initially hidden (#32457)

In a hidden iframe, `document.body.clientHeight` is not reliable. Use
`IntersectionObserver` to detect the visibility change and update the
height there.

Fixes: https://github.com/go-gitea/gitea/issues/32392

<img width="885" alt="image"
src="https://github.com/user-attachments/assets/a95ef6aa-27e7-443f-9d06-400ef27919ae">
pull/32460/head^2
silverwind 5 days ago committed by GitHub
parent 18aeca5320
commit b55a31eb6a
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  1. 13
      web_src/js/markup/mermaid.ts

@ -57,10 +57,21 @@ export async function renderMermaid() {
btn.setAttribute('data-clipboard-text', source);
mermaidBlock.append(btn);
const updateIframeHeight = () => {
iframe.style.height = `${iframe.contentWindow.document.body.clientHeight}px`;
};
// update height when element's visibility state changes, for example when the diagram is inside
// a <details> + <summary> block and the <details> block becomes visible upon user interaction, it
// would initially set a incorrect height and the correct height is set during this callback.
(new IntersectionObserver(() => {
updateIframeHeight();
}, {root: document.documentElement})).observe(iframe);
iframe.addEventListener('load', () => {
pre.replaceWith(mermaidBlock);
mermaidBlock.classList.remove('tw-hidden');
iframe.style.height = `${iframe.contentWindow.document.body.clientHeight}px`;
updateIframeHeight();
setTimeout(() => { // avoid flash of iframe background
mermaidBlock.classList.remove('is-loading');
iframe.classList.remove('tw-invisible');

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