Javascript Array getUnionStr(filed,split)

Array.prototype.getUnionStr=function(filed,split){
 //if(!(filed instanceof String))return "";
 try{//from   w w w . j a  v  a2  s .co m
 //if(!filed.isString())return "";
 var unionStr=new String();
 if(!split){
  split=",";
 }
 for(var i=0;i<this.length;i++){
  var tempVal=this[i][filed];
  //if(!tempVal.isString())continue;
  unionStr+=tempVal+split;
 }
  unionStr=unionStr.substr(0,unionStr.lastIndexOf(split));
 return unionStr;
 }catch(ex){alert(ex);}
}