paulirish

What forces layout / reflow

All of the below properties or methods, when requested/called in JavaScript, will trigger the browser to synchronously calculate the style and layout*. This is also called reflow or layout thrashing, and is common performance bottleneck.

Generally, all APIs that synchronously provide layout metrics will trigger forced reflow / layout. Read on for additional cases and details.

Element APIs

Getting box metrics

• elem.offsetLeft, elem.offsetTop, elem.offsetWidth, elem.offsetHeight, elem.offsetParent

paulirish

// selectorSupported lovingly lifted from the mad italian genius, diego perini
// http://javascript.nwbox.com/CSSSupport/
function selectorSupported(selector){
  
  var support, link, sheet, doc = document,
      root = doc.documentElement,
      head = root.getElementsByTagName('head')[0],

      impl = doc.implementation || {