cortex.js

/* vim:set ts=2 sw=2 sts=2
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Initial Developer of the Original Code is Mozilla.
 * Portions created by the Initial Developer are Copyright (C) 2010
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Irakli Gozalishvili <gozala@mozilla.com> (Original author)
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
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 * decision by deleting the provisions above and replace them with the notice
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 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */
(function() {
// Assigns `value` to the `object`'s property, where `name` is a name of the
  "use strict";
  
  // `var` is being used in the module in order to make it reusable in
  // environments in which `let` and `const` is not yet supported.
  
  // Returns `object`'s property value, where `name` is a name of the property.
  function get(object, name) {
    return object[name];
  }
  
  // property.
  function set(object, name, value) {
    return object[name] = value;
  }
  
  // Function takes `object` containing property with the given `name` and
  // creates alias property descriptor that can be used to define alias / proxy
  // properties on other objects. Value change on any alias will propagate to the
  // aliased property and other way round.
  function createAliasProperty(object, name) {
    // Getting own property descriptor of an `object` for the given `name` as
    // we are going to create proxy analog.
    var property = Object.getOwnPropertyDescriptor(object, name);
    var descriptor = {
      configurable: property.configurable,
      enumerable: property.enumerable,
      alias: true
    };
    // If original property has a getter using it's `object` bounded copy.
    // This way `this` pseudo-variable will alway be a `object`.
    if ("get" in property)
      descriptor.get = property.get.bind(object);
    // If original property has a setter using it's `object` bounded copy.
    if ("set" in property)
      descriptor.set = property.set.bind(object)
    
    // If original property was a value property.
    if ("value" in property) {
      // If original property is a method using it's `object` bounded copy.
      if (typeof property.value === "function") {
        descriptor.value = property.value.bind(object);
        // Also preserving writability of the original property.
        descriptor.writable = property.writable;
      }
      // If original property was just a data property we create a proxy
      // accessors to it propagate to changes to the original `object` and
      // other way round.
      else {
        descriptor.get = get.bind(null, object, name);
        descriptor.set = set.bind(null, object, name);
      }
    }
    return descriptor;
  }
  this.createAliasProperty = createAliasProperty;
  
  // Defines property on `object` object with a name `alias` if given if not
  // defaults to `name` that represents an alias of `source[name]`. If aliased
  // property was an assessor or a method `this` pseudo-variable will be `source`
  // when invoked. If aliased property was a data property changes on any of the
  // aliases will propagate to the `source[name]` and also other way round.
  function defineAlias(target, source, name, alias) {
    return Object.defineProperty(target, alias || name,
                                         createAliasProperty(source, name));
  }
  this.defineAlias = defineAlias;
  
  this.cortex = function cortex(object, names, prototype) {
    // Creating a cortex object from the given `prototype`, if one was not
    // provided then `prototype` of a given `object` is used. This allows
    // consumer to define expected behavior `instanceof`. In common case
    // `prototype` argument can be omitted to preserve same behavior of
    // `instanceof` as on original `object`.
    var cortex = Object.create(prototype || Object.getPrototypeOf(object));
    // Creating alias properties on the `cortex` object for all the own
    // properties of the original `object` that are contained in `names` array.
    // If `names` array is not provided then all the properties that don't
    // start with `"_"` are aliased.
    Object.getOwnPropertyNames(object).forEach(function (name) {
      if ((!names && "_" !== name.charAt(0)) || (names && ~names.indexOf(name)))
        defineAlias(cortex, object, name);
    });
    return cortex;
  }
}).call(window);