layout/style/test/test_animations_dynamic_changes.html

<!DOCTYPE HTML>
<html>
<!--
https://bugzilla.mozilla.org/show_bug.cgi?id=978833
-->
<head>
  <title>Test for Bug 978833</title>
  <script src="/tests/SimpleTest/SimpleTest.js"></script>
  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
  <style id="style">
  @keyframes a {
    from, to {
      /* a non-inherited property, so it's cached in the rule tree */
      margin-left: 50px;
    }
  }
  .alwaysa {
    animation: a linear 1s infinite;
  }
  </style>
</head>
<body>
<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=978833">Mozilla Bug 978833</a>
<p id="display"></p>
<pre id="test">
<script type="application/javascript">

var p = document.getElementById("display");
var cs = getComputedStyle(p, "");
var style = document.getElementById("style").sheet;

/** Test for Bug 978833 **/
function test_bug978833() {
  var kfs = style.cssRules[0];
  var kf = kfs.cssRules[0];
  is(kf.style.marginLeft, "50px", "we found the right keyframe rule");

  p.classList.add("alwaysa");
  is(cs.marginLeft, "50px", "p margin-left should be 50px");

  // Temporarily remove the animation style, since we resolve keyframes
  // on top of current animation styles (although maybe we shouldn't),
  // so we need to remove those styles to hit the rule tree cache.
  p.classList.remove("alwaysa");
  is(cs.marginLeft, "0px", "p margin-left should be 0px without animation");

  p.classList.add("alwaysa");
  kf.style.marginLeft = "100px";
  is(cs.marginLeft, "100px", "p margin-left should be 100px after change");

  // Try the same thing a second time, just to make sure it works again.
  p.classList.remove("alwaysa");
  is(cs.marginLeft, "0px", "p margin-left should be 0px without animation");
  p.classList.add("alwaysa");
  kf.style.marginLeft = "150px";
  is(cs.marginLeft, "150px", "p margin-left should be 150px after second change");

  p.style.animation = "";
}
test_bug978833();

</script>
</pre>
</body>
</html>