Batched Reflows

JavaScript performance comparison

Revision 4 of this test case created

Info

When making a number of style changes that trigger reflow, is it better to hide the element before making the changes, and then show it again after the changes are complete?

Preparation code

<div id="my-wrapper">
  Test DIV
</div>
<script>
  var myWrapper = document.getElementById('my-wrapper');
</script>

Preparation code output

Test DIV

Test runner

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Testing in unknown unknown
Test Ops/sec
Separate Reflows
 
// first add the list, for testing purposes
myWrapper.innerHTML = '<ul id="my-list"><li></li><li></li><li></li><li></li><li></li><li></li><li></li><li></li><li></li><li></li></ul>';

myList = document.getElementById('my-list');
for (var i = 0, len = myList.childNodes.length; i < len; i++) {
  var thisChild = myList.childNodes[i];
  if (thisChild.nodeType == 1) {
    thisChild.style.height = '50px';
    thisChild.style.padding = '15px';
  }
}
// remove the list for testing purposes
myWrapper.innerHTML = '';
 pending…
Batched Reflows
 
// first add the list, for testing purposes
myWrapper.innerHTML = '<ul id="my-list"><li></li><li></li><li></li><li></li><li></li><li></li><li></li><li></li><li></li><li></li></ul>';

myList = document.getElementById('my-list');
myList.style.display = 'none';
for (var i = 0, len = myList.childNodes.length; i < len; i++) {
  var thisChild = myList.childNodes[i];
  if (thisChild.nodeType == 1) {
    thisChild.style.height = '50px';
    thisChild.style.padding = '15px';
  }
}
myList.style.display = 'block';
// remove the list for testing purposes
myWrapper.innerHTML = '';
 pending…

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