getComputedStyle for IE

getComputedStyle.js

function getIEComputedStyle(elem, prop) {
  var value = elem.currentStyle[prop] || 0

  // we use 'left' property as a place holder so backup values
  var leftCopy = elem.style.left
  var runtimeLeftCopy = elem.runtimeStyle.left

  // assign to runtimeStyle and get pixel value
  elem.runtimeStyle.left = elem.currentStyle.left
  elem.style.left = (prop === "fontSize") ? "1em" : value
  value = elem.style.pixelLeft + "px";

  // restore values for left
  elem.style.left = leftCopy 
  elem.runtimeStyle.left = runtimeLeftCopy 
 
  return value
}