detect html document if it has right-to-left layout, even if direction is provided using css and not as an attribute.

isRtl.js

/**
 * polyfill `getComputedStyle` in IE
 */

window.getComputedStyle = window.getComputedStyle || function( element ) {
  return element.currentStyle;
}

/**
 * detect RTL layout
 */

function isRtl() {
  var html = document.documentElement;
  var style = getComputedStyle( html );
  
  return style.direction === 'rtl';
}