wpt/css/css-contain/content-visibility/content-visibility-auto-first-observation-immediate.html at master · web-platform-tests/wpt · GitHub

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<!doctype HTML>
<html>
<meta charset="utf8">
<title>Content Visibility: first visibility determination happens before resize observer.</title>
<link rel="author" title="Vladimir Levin" href="mailto:vmpstr@chromium.org">
<link rel="help" href="https://drafts.csswg.org/css-contain/#content-visibility">
<meta name="assert" content="first visibility determination happens before resize observer">

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<style>
#target {
  content-visibility: auto;
  contain-intrinsic-size: 10px;
}
#child {
  height: 100px;
}
</style>

<div id=container></div>

<script>
promise_test(t => new Promise(async (resolve, reject) => {
  requestAnimationFrame(() => {
    let target = document.createElement("div");
    target.id = "target";

    let child = document.createElement("div");
    child.id = "child";
    target.appendChild(child);

    const resizeObserver = new ResizeObserver((entries) => {
      for (const entry of entries) {
        if (entry.contentBoxSize) {
          if (entry.contentBoxSize[0].blockSize == 100) {
            resolve();
            return;
          } else {
            reject(`unexpected size ${entry.contentBoxSize[0].blockSize}`);
            return;
          }
        }
      }
      reject("no content boxes or no entries");
    });

    container.appendChild(target);
    resizeObserver.observe(target);
  });
}), "Target is sized and laid out before resize observer");
</script>