Why is IE9 Another Thorn in our Side?

which form.js

/* 
 * margin-top or marginTop? 
 * When to use lower-case and camel-case property names in JavaScript.
 */

// Setting style: camel-case
elem.style.marginTop = '10px';

// Getting style: camel-case
var value = elem.style.marginTop;

// Getting computed style: lower-case
var value =
  window.getComputedStyle(elem).getPropertyValue( 'margin-top' );

/* Vendor prefixed properties are slightly different */

// Setting or getting style: camel-case with leading upper-case
elem.style.MozTransform = "rotate(90deg)";
// or WebkitTransform or OTransform

// Getting computed style: lower-case with leading dash
var value = 
  window.getComputedStyle(elem).getPropertyValue( '-moz-transform' );
// or "-webkit-transform" or "-o-transform"

/* Trickier: setting the transition property */

// mixed camel-case and lower-case
elem.style.MozTransition =
  "margin-top 1s ease, -moz-transform 1s linear";

/* Too complex?
 * No worries, JavaScript libraries can handle that for you 
 */

// Setting style with jQuery: any form can be used 
$( elem ).css( 'margin-top', '10px' );
// Getting computed style with jQuery: any form can be used
$( elem ).css( 'marginTop' );
// Even with vendor prefixed properties
$( elem ).css( 'MozTransform' );

/* Conversion is actually really easy using regular expressions */

function camelCase( name ) {
  return name.replace(/-([a-z])/g, function( all, letter ) {
    return letter.toUpperCase();
  });
}

function lowerCase( name ) {
  return name.replace(/([A-Z])/g, "-$1").toLowerCase();
}

/* 
 * They work both for "standard" properties AND vendor prefixed ones!
 * ...
 * Introducing IE9
 */

// Setting and Getting style: camel case without leading upper-case!
elem.style.msTransform = "rotate(90deg)";

/* Thought dirty browser-specific workarounds were a thing of the past? 
 * Think again.
 */

function fixedCamelCase( name ) {
  if ( name.indexOf('-ms-') === 0 ) {
    name = name.substr(1);
  }
  return name.replace(/-([a-z])/g, function( all, letter ) {
    return letter.toUpperCase();
  });
}

function fixedLowerCase( name ) {
  return name.replace(/([A-Z]|^ms)/g, "-$1").toLowerCase();
}

/* Thank god there are no style properties starting with "ms..." */

@louis_remi