Helpers for creating extendable JavaScript objects

extendable.js

function extend() {
  var result = arguments[0];
  for(var i = 1; i < arguments.length; i++) {
    for(var key in arguments[i]) {
      result[key] = arguments[i][key];
    }
  }
  return result;
}

function toArray(array) {
  return Array.prototype.slice.call(array);
}

function extendable(obj) {
  return extend(obj, {
    extend: function() {
      return extend.apply(this, [{}, this.valueOf()].concat(toArray(arguments)));
    }
  });
}