test_img_src_causing_reflow.html

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<!doctype html>

<meta charset="utf-8">

<title>Test for bug 1787072</title>

<script src="/tests/SimpleTest/SimpleTest.js"></script>

<style>

img {

  width: 100px;

  height: 100px;

  background-color: blue;

</style>

<img> <!-- Initially broken -->

<script>

add_task(async function() {

  const utils = SpecialPowers.DOMWindowUtils;

  const img = document.querySelector("img");

  img.getBoundingClientRect();

  let origFramesConstructed = utils.framesConstructed;

  let origFramesReflowed = utils.framesReflowed;

  let error = new Promise(r => img.addEventListener("error", r, { once: true }));

  // Doesn't need to be an actual image.

  img.src = "/some-valid-url";

  img.getBoundingClientRect();

  is(origFramesReflowed, utils.framesReflowed, "Shouldn't have reflowed when going broken -> loading");

  is(origFramesConstructed, utils.framesConstructed, "Shouldn't have reflowed when going broken -> loading");

  await error;

  is(origFramesReflowed, utils.framesReflowed, "Shouldn't have reflowed when going loading -> broken");

  is(origFramesConstructed, utils.framesConstructed, "Shouldn't have reflowed when going loading -> broken");

});

</script>