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HTML

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CSS

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JavaScript

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HTML 

              
                <h1>Webkit style recalc bug</h1>
<p>Webkit seems to have a nasty bug that causes <strong>MAJOR</strong> slowdowns if you merely read a property from the calculated style after setting an inline value on a completely different element altogether, even of the property doesn't affect document flow at all (<code>WebkitTransform</code> in this case). It forces a style recalc but it really shouldn't. Or am I missing something? 
  
  
  When you click "run test" below, we'll loop through all the letters, <code>getCalculatedStyle()</code> on each one, and then set the <code>style.WebkitTransform</code> to a random offset. Watch how much longer it takes if you select "Read transform before setting"! I know it'll go faster if all of the reading happens first, and then all of the setting, but that shouldn't be necessary.</p>
<label style="color:red"><input type="checkbox" id="read" /> Read transform before setting</label><br> <button>RUN TEST</button>
<div id="time"></div>
<div id="container"></div>
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CSS 

              
                body {
  background-color: black;
  color: #ccc;
  font-family: sans-serif;
}
h1 {
  color: white;
  font-weight: normal;
}
#container {
  font-size:25px;
  color: #555;
  margin-top: 15px;
}
div {
  display:inline-block;
  position:relative;
}
button {
  font-size: 20px;
  padding: 10px;
}
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JS 

              
                var letters = "abcdefghijklmnopqrstuvwxyz",
    i = 2000, //number of letters (increase to add stress)
    container = document.getElementById("container"),
    content = [],
    div;

//create a bunch of DIVs with a random letter in each...
while (--i > -1) {
  div = document.createElement("div");
  container.appendChild(div);
  div.innerHTML = letters.charAt(getRandomInt(0,26));
  content.push(div);
}

$("button").click(function() {
  var time = Date.now(),
      i = content.length,
      read = $("#read").prop("checked"),
      newValue = "translate(" + getRandomInt(0, 100) + "px," + getRandomInt(0, 100) + "px)",
      computedStyle,
      currentTransform;
  while (--i > -1) {
    computedStyle = document.defaultView.getComputedStyle(content[i]);
    if (read) { //LOOK HOW MUCH LONGER THIS TAKES (and we're not really doing anything except reading a property)
      currentTransform = computedStyle.WebkitTransform;
    }
    content[i].style.WebkitTransform = newValue;
  }
  $("#time").text("took " + (Date.now() - time) + "ms");
});

function getRandomInt(min, max) {
  return Math.round(min + (Math.random() * (max - min)));
}
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999px

Console