Nodejs Utililty Methods Array Join

function foo(arr)
    var o2 = o;
    var y = 100;
    for (var i =0;i<10;i++)
        y += o2.x + arr;
    WScript.Echo(y);
...

Array.prototype.join = function(separator) {
  var s = new String();
  for (var i = 0, len = this.length; i < len; i++) {
    s += (i > 0) ? separator : "";
    s += (typeof this[i] == "object" && this[i].constructor === Array) ? this[i].join(separator) : this[i];
  return s;
};

Array.prototype.joinModel = function(id_app,model,joinFields,fn){
  var array = this;  
  async.map(array,function(a,callback){
    async.map(joinFields,function(join,callback){
      var akey = join.akey;
      var bkey = join.bkey;
      var avalue = a[akey];
      var query = {id_app:id_app};
      query[bkey] = avalue;
...

Array.prototype.joinsub = function (array, sizediff) {
  if (!array)
    return null;
  var match = [];
  for (var i = 0; i < this.length; i++) {
    if (this[i].contains(array, sizediff)) {
      for (var j = 0; j < this[i].length; j++) {
        if (array.indexOf(this[i][j]) == -1) {
            match.push(this[i][j]);
...