Javascript Code Challenge

jcc.js

Array.prototype.joinProperty = function(delim,method) {
    var output = '';

    for(var i=0; i < this.length; i++){
      if(this[i].hasOwnProperty(method)){
       output = output.concat(this[i][method],delim);
     }else if(eval("typeof this[i]."+method+" != 'undefined'")){
       output = output.concat(eval('this[i].'+method+'()'),delim);
     }
   }
   return output.slice(0,output.length-delim.length);
 }