Array.prototype.join

/*
JScript does not default the separator to “,” if the separator value is undefined.
*/
	var array = [1, 2];
	alert(array.join());
	alert(array.join(undefined));
	alert(array.join('-'));
/*
Output: 
     IE: 1,2 1undefined2 1-2
     FF: 1,2 1,2 1-2 
  Opera: same as FF 
 Safari: same as FF
*/