| <!DOCTYPE html> |
| <title>Layout Instability: shift while scrolled</title> |
| <link rel="help" href="https://wicg.github.io/layout-instability/" /> |
| <style> |
| |
| body { height: 2000px; margin: 0; } |
| #shift { position: relative; width: 300px; height: 200px; } |
| |
| </style> |
| <div id="shift"></div> |
| <script src="/resources/testharness.js"></script> |
| <script src="/resources/testharnessreport.js"></script> |
| <script src="resources/util.js"></script> |
| <script> |
| |
| promise_test(async () => { |
| const watcher = new ScoreWatcher; |
| |
| // Wait for the initial render to complete. |
| await waitForAnimationFrames(2); |
| |
| // Scroll down by 100px. |
| document.scrollingElement.scrollTop = 100; |
| assert_equals(watcher.score, 0); |
| |
| // Generate a layout shift. |
| document.querySelector("#shift").style = "top: 60px"; |
| |
| // Impact region: width * (height - scrollTop + moveDistance) |
| const expectedScore = computeExpectedScore( |
| 300 * (200 - 100 + 60), 60); |
| |
| await watcher.promise; |
| assert_equals(watcher.score, expectedScore); |
| }, 'Layout shift with non-zero scroll offset.'); |
| |
| </script> |
