michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: "use strict";
michael@0: 
michael@0: module.metadata = {
michael@0:   "stability": "deprecated"
michael@0: };
michael@0: 
michael@0: // `var` is being used in the module in order to make it reusable in
michael@0: // environments in which `let` and `const` is not yet supported.
michael@0: 
michael@0: // Returns `object`'s property value, where `name` is a name of the property.
michael@0: function get(object, name) {
michael@0:   return object[name];
michael@0: }
michael@0: 
michael@0: // Assigns `value` to the `object`'s property, where `name` is the name of the
michael@0: // property.
michael@0: function set(object, name, value) {
michael@0:   return object[name] = value;
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * Given an `object` containing a property with the given `name`, create
michael@0:  * a property descriptor that can be used to define alias/proxy properties
michael@0:  * on other objects.  A change in the value of an alias will propagate
michael@0:  * to the aliased property and vice versa.
michael@0:  */
michael@0: function createAliasProperty(object, name) {
michael@0:   // Getting own property descriptor of an `object` for the given `name` as
michael@0:   // we are going to create proxy analog.
michael@0:   var property = Object.getOwnPropertyDescriptor(object, name);
michael@0:   var descriptor = {
michael@0:     configurable: property.configurable,
michael@0:     enumerable: property.enumerable,
michael@0:     alias: true
michael@0:   };
michael@0: 
michael@0:   // If the original property has a getter and/or setter, bind a
michael@0:   // corresponding getter/setter in the alias descriptor to the original
michael@0:   // object, so the `this` object in the getter/setter is the original object
michael@0:   // rather than the alias.
michael@0:   if ("get" in property && property.get)
michael@0:     descriptor.get = property.get.bind(object);
michael@0:   if ("set" in property && property.set)
michael@0:     descriptor.set = property.set.bind(object);
michael@0:   
michael@0:   // If original property was a value property.
michael@0:   if ("value" in property) {
michael@0:     // If original property is a method using it's `object` bounded copy.
michael@0:     if (typeof property.value === "function") {
michael@0:       descriptor.value = property.value.bind(object);
michael@0:       // Also preserving writability of the original property.
michael@0:       descriptor.writable = property.writable;
michael@0:     }
michael@0: 
michael@0:     // If the original property was just a data property, we create proxy
michael@0:     // accessors using our custom get/set functions to propagate changes to the
michael@0:     // original `object` and vice versa.
michael@0:     else {
michael@0:       descriptor.get = get.bind(null, object, name);
michael@0:       descriptor.set = set.bind(null, object, name);
michael@0:     }
michael@0:   }
michael@0:   return descriptor;
michael@0: }
michael@0: 
michael@0: // Defines property on `object` object with a name `alias` if given if not
michael@0: // defaults to `name` that represents an alias of `source[name]`. If aliased
michael@0: // property was an assessor or a method `this` pseudo-variable will be `source`
michael@0: // when invoked. If aliased property was a data property changes on any of the
michael@0: // aliases will propagate to the `source[name]` and also other way round.
michael@0: function defineAlias(source, target, name, alias) {
michael@0:   return Object.defineProperty(target, alias || name,
michael@0:                                createAliasProperty(source, name));
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * Function takes any `object` and returns a proxy for its own public
michael@0:  * properties. By default properties are considered to be public if they don't
michael@0:  * start with `"_"`, but default behavior can be overridden if needed, by
michael@0:  * passing array of public property `names` as a second argument. By default
michael@0:  * returned object will be direct decedent of the given `object`'s prototype,
michael@0:  * but this can be overridden by passing third optional argument, that will be
michael@0:  * used as `prototype` instead.
michael@0:  * @param {Object} object
michael@0:  *    Object to create cortex for.
michael@0:  * @param {String[]} [names]
michael@0:  *    Optional array of public property names.
michael@0:  * @param {Object} [prototype]
michael@0:  *    Optional argument that will be used as `prototype` of the returned object,
michael@0:  *    if not provided `Object.getPrototypeOf(object)` is used instead.
michael@0:  */
michael@0: exports.Cortex = function Cortex(object, names, prototype) {
michael@0:   // Creating a cortex object from the given `prototype`, if one was not
michael@0:   // provided then `prototype` of a given `object` is used. This allows
michael@0:   // consumer to define expected behavior `instanceof`. In common case
michael@0:   // `prototype` argument can be omitted to preserve same behavior of
michael@0:   // `instanceof` as on original `object`.
michael@0:   var cortex = Object.create(prototype || Object.getPrototypeOf(object));
michael@0:   // Creating alias properties on the `cortex` object for all the own
michael@0:   // properties of the original `object` that are contained in `names` array.
michael@0:   // If `names` array is not provided then all the properties that don't
michael@0:   // start with `"_"` are aliased.
michael@0:   Object.getOwnPropertyNames(object).forEach(function (name) {
michael@0:     if ((!names && "_" !== name.charAt(0)) || (names && ~names.indexOf(name)))
michael@0:       defineAlias(object, cortex, name);
michael@0:   });
michael@0:   return cortex;
michael@0: }