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chore: DRY out preload link/header logic #16445

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elliott-with-the-longest-name-on-github merged 2 commits into from
Jul 20, 2026
+19 −28
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chore: DRY out preload link/header logic #16445

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3723b42
chore: DRY out preload link/header logic
Rich-Harris Jul 20, 2026
a9ae4af
Fix: The user-provided `resolve_opts.preload` hook is invoked twice p…
vercel[bot] Jul 20, 2026
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47 changes: 19 additions & 28 deletions packages/kit/src/runtime/server/page/render.js
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Original file line number Diff line number Diff line change
Expand Up @@ -304,6 +304,19 @@ export async function render_response({
head.add_style(style, attributes);
}

/**
* see the `output.linkHeaderPreload` option for details on why we have multiple options here
* @param {string} path
* @param {string[]} attributes
*/
const add_preload = (path, attributes) => {
if (options.link_header_preload && !state.prerendering) {
link_headers.add(`<${encodeURI(path)}>; ${attributes.join('; ')}; nopush`);
} else {
head.add_link_tag(path, attributes);
}
};

for (const dep of stylesheets) {
const path = prefixed(dep);

Expand All @@ -328,18 +341,7 @@ export async function render_response({
if (resolve_opts.preload({ type: 'font', path })) {
const ext = dep.slice(dep.lastIndexOf('.') + 1);

if (options.link_header_preload && !state.prerendering) {
link_headers.add(
`<${encodeURI(path)}>; rel="preload"; as="font"; type="font/${ext}"; crossorigin; nopush`
);
} else {
head.add_link_tag(path, [
'rel="preload"',
'as="font"',
`type="font/${ext}"`,
'crossorigin'
]);
}
add_preload(path, ['rel="preload"', 'as="font"', `type="font/${ext}"`, 'crossorigin']);
}
}

Expand Down Expand Up @@ -368,23 +370,12 @@ export async function render_response({
}

if (!client.inline) {
const included_modulepreloads = Array.from(modulepreloads, (dep) => prefixed(dep)).filter(
(path) => resolve_opts.preload({ type: 'js', path })
);

/** @type {(path: string) => void} */
let add_preload;
for (const dep of modulepreloads) {
const path = prefixed(dep);

// see the output.preloadStrategy option for details on why we have multiple options here
if (options.link_header_preload && !state.prerendering) {
add_preload = (path) =>
link_headers.add(`<${encodeURI(path)}>; rel="modulepreload"; nopush`);
} else {
add_preload = (path) => head.add_link_tag(path, ['rel="modulepreload"']);
}

for (const path of included_modulepreloads) {
add_preload(path);
if (resolve_opts.preload({ type: 'js', path })) {
add_preload(path, ['rel="modulepreload"']);
}
}
}

Expand Down
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