// TODO: in future try to replace most inline compability checks with polyfills for code readability 

// element.textContent polyfill.
// Unsupporting browsers: IE8

if (Object.defineProperty && Object.getOwnPropertyDescriptor && Object.getOwnPropertyDescriptor(Element.prototype, "textContent") && !Object.getOwnPropertyDescriptor(Element.prototype, "textContent").get) {
	(function() {
		var innerText = Object.getOwnPropertyDescriptor(Element.prototype, "innerText");
		Object.defineProperty(Element.prototype, "textContent",
			{
				get: function() {
					return innerText.get.call(this);
				},
				set: function(s) {
					return innerText.set.call(this, s);
				}
			}
		);
	})();
}

// isArray polyfill for ie8
if(!Array.isArray) {
  Array.isArray = function(arg) {
    return Object.prototype.toString.call(arg) === '[object Array]';
  };
}
// TODO: in future try to replace most inline compability checks with polyfills for code readability 

// IE8 SUPPORT BLOCK
// You can compile wuthout all this if IE8 is not needed

// addEventListener, removeEventListener
// TODO: make usage of wysihtml5.dom.observe obsolete
(function() {
  if (!Event.prototype.preventDefault) {
    Event.prototype.preventDefault=function() {
      this.returnValue=false;
    };
  }
  if (!Event.prototype.stopPropagation) {
    Event.prototype.stopPropagation=function() {
      this.cancelBubble=true;
    };
  }
  if (!Element.prototype.addEventListener) {
    var eventListeners=[];
    
    var addEventListener=function(type,listener /*, useCapture (will be ignored) */) {
      var self=this;
      var wrapper=function(e) {
        e.target=e.srcElement;
        e.currentTarget=self;
        if (listener.handleEvent) {
          listener.handleEvent(e);
        } else {
          listener.call(self,e);
        }
      };
      if (type=="DOMContentLoaded") {
        var wrapper2=function(e) {
          if (document.readyState=="complete") {
            wrapper(e);
          }
        };
        document.attachEvent("onreadystatechange",wrapper2);
        eventListeners.push({object:this,type:type,listener:listener,wrapper:wrapper2});
        
        if (document.readyState=="complete") {
          var e=new Event();
          e.srcElement=window;
          wrapper2(e);
        }
      } else {
        this.attachEvent("on"+type,wrapper);
        eventListeners.push({object:this,type:type,listener:listener,wrapper:wrapper});
      }
    };
    var removeEventListener=function(type,listener /*, useCapture (will be ignored) */) {
      var counter=0;
      while (counter<eventListeners.length) {
        var eventListener=eventListeners[counter];
        if (eventListener.object==this && eventListener.type==type && eventListener.listener==listener) {
          if (type=="DOMContentLoaded") {
            this.detachEvent("onreadystatechange",eventListener.wrapper);
          } else {
            this.detachEvent("on"+type,eventListener.wrapper);
          }
          eventListeners.splice(counter, 1);
          break;
        }
        ++counter;
      }
    };
    Element.prototype.addEventListener=addEventListener;
    Element.prototype.removeEventListener=removeEventListener;
    if (HTMLDocument) {
      HTMLDocument.prototype.addEventListener=addEventListener;
      HTMLDocument.prototype.removeEventListener=removeEventListener;
    }
    if (Window) {
      Window.prototype.addEventListener=addEventListener;
      Window.prototype.removeEventListener=removeEventListener;
    }
  }
})();

// element.textContent polyfill.
if (Object.defineProperty && Object.getOwnPropertyDescriptor && Object.getOwnPropertyDescriptor(Element.prototype, "textContent") && !Object.getOwnPropertyDescriptor(Element.prototype, "textContent").get) {
	(function() {
		var innerText = Object.getOwnPropertyDescriptor(Element.prototype, "innerText");
		Object.defineProperty(Element.prototype, "textContent",
			{
				get: function() {
					return innerText.get.call(this);
				},
				set: function(s) {
					return innerText.set.call(this, s);
				}
			}
		);
	})();
}

// isArray polyfill for ie8
if(!Array.isArray) {
  Array.isArray = function(arg) {
    return Object.prototype.toString.call(arg) === '[object Array]';
  };
}

// Function.prototype.bind()
// TODO: clean the code from variable 'that' as it can be confusing
if (!Function.prototype.bind) {
  Function.prototype.bind = function(oThis) {
    if (typeof this !== 'function') {
      // closest thing possible to the ECMAScript 5
      // internal IsCallable function
      throw new TypeError('Function.prototype.bind - what is trying to be bound is not callable');
    }

    var aArgs   = Array.prototype.slice.call(arguments, 1),
        fToBind = this,
        fNOP    = function() {},
        fBound  = function() {
          return fToBind.apply(this instanceof fNOP && oThis
                 ? this
                 : oThis,
                 aArgs.concat(Array.prototype.slice.call(arguments)));
        };

    fNOP.prototype = this.prototype;
    fBound.prototype = new fNOP();

    return fBound;
  };
}
Add some useful IE8 polyfills for refactoring to better progressive-enhancement