Compatibility issues related to dom and xml node access under javascript_javascript skills

var isIE = ????;
//Global variable, determine whether IE, self-improvement
// new dom method
function parseXML(st){
if ( isIE){
var result = new ActiveXObject( "microsoft.XMLDOM" );
result.loadXML(st);
} else {
var parser = new DOMParser();
var result = parser.parseFromString(st, "text/xml" );
}
return result;
}
if (! isIE){
var ex;
// Definition Node xml attribute
XMLDocument.prototype.__proto__.__defineGetter__( "xml" , function (){
try {
return new XMLSerializer().serializeToString( this );
          } catch (ex){
var d = document.createElement("div");
d.appendChild(this .cloneNode(true));
return d.innerHTML;                                                                                                                                     > Element.prototype.__proto__.__defineGetter__( "xml" , function (){
try {
return new XMLSerializer().serializeToString(this);
} c atch (ex){
var d = document.createElement( "div" );
d.appendChild( this .cloneNode( true ));
return d.innerHTML;
}
//Define nodes text attribute
"text" , function (){
return this .textContent
});
// Define selectSingleNode, selectNodes methods
XMLDocument.prototype.selectSingleNode = Element.prototype.selectSingle Node = function (xpath){
var x = this .selectNodes(xpath)
if ( ! x || x.length < 1 ) return null ;
return x[0];
} 
    XMLDocument.prototype.selectNodes = Element.prototype.selectNodes = function (xpath){ 
         var  xpe  =   new  XPathEvaluator(); 
         var  nsResolver  =  xpe.createNSResolver( this .ownerDocument  ==   null   ?  
             this .documentElement :  this .ownerDocument.documentElement); 
         var  result  =  xpe.evaluate(xpath,  this , nsResolver,  0 ,  null ); 
         var  found  =  []; 
         var  res; 
         while  (res  =  result.iterateNext()) 
            found.push(res); 
         return  found; 
    } 

}