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- This WPT test may be referenced by the following Test IDs:
- /resource-timing/cached-image-gets-single-entry.html - WPT Dashboard Interop Dashboard
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Resource Timing: test behavior for cached resources</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/observe-entry.js"></script>
</head>
<body>
<h1>Description</h1>
<p>Test that a reused resource only appears in the buffer once.</p>
<script>
// Need our own image loading helper because the one in resource-loaders.js
// is desgined to always side-step the HTTP cache but this test relies on the
// second request being resolved from the cache.
const load_image = path => new Promise(resolve => {
const img = document.createElement('img');
img.onload = img.onerror = () => resolve();
img.src = path;
document.body.append(img);
});
promise_test(async () => {
const blue = "resources/blue.png";
// First request. Should appear in the timeline.
await load_image(blue + "?cacheable");
// Second request. Should not appear in the timeline.
await load_image(blue + "?cacheable");
// Third request. When this request shows up in the timeline, we know that, if
// the second request would generate an entry, that entry would have already
// shown up in the timeline. Without this, we'd need to guess at how long to
// wait which tends to be flaky.
await load_image(blue + "?avoid-cache");
const entries = await new Promise(resolve => {
const accumulator = [];
new PerformanceObserver(entry_list => {
entry_list.getEntries().forEach(entry => {
if (!entry.name.includes("blue.png")) {
// Ignore resources other than blue images.
return;
}
accumulator.push(entry);
// Once we see the 'canary' resource, we don't need to wait anymore.
if (entry.name.endsWith('avoid-cache')) {
resolve(accumulator);
}
});
}).observe({'type': 'resource', 'buffered': true});
});
assert_equals(entries.length, 2, "There must be exactly 2 entries in the " +
"Performance Timeline");
assert_true(entries[0].name.endsWith("blue.png?cacheable"));
assert_true(entries[1].name.endsWith("blue.png?avoid-cache"));
}, "When a resource is resolved from cache, there must not be a " +
"corresponding entry in the Performance Timeline");
</script>
</body>
</html>