Skel `each`

_.mixin([_.ARRAY, _.OBJECT], {
  each: function(collection, iterator) {
    var error = [];
    if (collection == null) error.push("_.each requires a collection parameter");
    if (typeof collection !== "object") error.push("_.each expects hash or array as first argument");
    if (iterator == null) error.push("_.each requires an iterator parameter (2nd parameter)");
    if (error.length > 0) {
      throw new Error(error.join(". "));
      return;
    }
    switch (iterator.length) { // the number of arguments that the iterator accepts
      case 0:
        for (var key in collection) {
          if (collection.hasOwnProperty(key)) {
            iterator.call(collection[key]);
          }
        }
        break;
      case 1:
        for (var key in collection) {
          if (collection.hasOwnProperty(key)) {
            iterator(collection[key]);
          }
        }
        break;
      case 2:
        for (var key in collection) {
          if (collection.hasOwnProperty(key)) {
            iterator(key, collection[key]);
          }
        }
        break;
    }
    return collection;
  }
});