Cross ECMAScript way to know if an object is an Arguments one. IE5+ and every other old or modern engine should simply work.

gistfile1.js

var isArguments = function(toString){
  // (C) WebReflection - Mit Style License
  var compare = toString.call(arguments);
  return ~compare.indexOf("Arguments") ?
    function isArguments(object) {
      return toString.call(object) == compare;
    } :
    (compare = toString.call([])) &&
    function isArguments(object) {
      try {
        return toString.apply(
          object, object
        ) != compare;
      } catch(o_O) {
        return false;
      }
    }
  ;
}({}.toString);