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respect limit when throttle is also set #503

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respect limit when throttle is also set #503

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f64d97f
respect `limit` when `throttle` is also set
rootkiller6788 Sep 17, 2026
e167231
add a regression test for limit + throttle
rootkiller6788 Sep 17, 2026
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7 changes: 6 additions & 1 deletion src/index.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,9 @@ export function listen(options = {}) {
const delay = options.delay || 0;
const hrefsInViewport = new Map();
const specRulesInViewport = new Map();
// Prefetches handed to the throttler that haven't started yet. `toPrefetch`
// only grows once a task runs, so queued work has to be reserved separately.
let scheduled = 0;

const timeoutFn = options.timeoutFn || requestIdleCallback;
const hrefFn = typeof options.hrefFn === 'function' && options.hrefFn;
Expand Down Expand Up @@ -174,8 +177,10 @@ export function listen(options = {}) {
}

// Do not prefetch if will match/exceed limit and user has not switched to shouldOnlyPrerender mode
if (toPrefetch.size < limit && !shouldOnlyPrerender) {
if (toPrefetch.size + scheduled < limit && !shouldOnlyPrerender) {
scheduled++;
toAdd(() => {
scheduled--;
prefetch(
hrefFn ? hrefFn(entry) : entry.href,
options.priority,
Expand Down
25 changes: 25 additions & 0 deletions test/fixtures/test-limit-throttle.html
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@@ -0,0 +1,25 @@
<!doctype html>
<html lang="en">

<head>
<meta charset="utf-8">
<title>Prefetch: Limit and throttle</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="main.css">
</head>

<body>
<a href="1.html">Link 1</a>
<a href="2.html">Link 2</a>
<a href="3.html">Link 3</a>
<a href="4.html">Link 4</a>
<script src="../../dist/quicklink.umd.js"></script>
<script>
quicklink.listen({
limit: 2,
throttle: 1,
});
</script>
</body>

</html>
18 changes: 18 additions & 0 deletions test/quicklink.spec.js
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Expand Up @@ -317,6 +317,24 @@ mainSuite('should not exceed the `limit` total', async context => {
assert.ok(ours.includes(`${server}/1.html`));
});

mainSuite('should not exceed the `limit` when `throttle` is also set', async context => {
const URLs = [];

context.handleRequest = async req => {
const url = req.url();
if (/test\/fixtures\/\d+\.html$/i.test(url)) {
URLs.push(url);
return req.respond({status: 200});
}

return req.continue();
};

await context.page.goto(`${server}/test-limit-throttle.html`);
await sleep();
assert.is(URLs.length, 2);
});

mainSuite('should respect the `throttle` concurrency', async context => {
const URLs = []; // Note: Page makes 4 requests

Expand Down
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