capabilities.js

/* ***** 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 Original Code is Jetpack.
 *
 * 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>
 *
 * 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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 *
 * ***** END LICENSE BLOCK ***** */

"use strict";

const { Trait } = require('traits/core');

function Get(key) this[key]
function Set(key, value) this[key] = value

/**
 * @see https://jetpack.mozillalabs.com/sdk/latest/docs/#module/jetpack-core/capabilities
 */
const PublicTrait = Trait.compose({
  /**
   * Lazy property that represents map of public property descriptors.
   * This property is a trait containing only subset of the API that is
   * can be safely used to construct objects that will be exposed as a
   * public API.
   * @see #_public
   */
  get _publicTrait() {
    let trait = {},
        keys = Object.getOwnPropertyNames(this);
    for each (let key in keys) {
      if ('_' === key.charAt(0) && '__iterator__' !== key )
        continue;
      let property = Object.getOwnPropertyDescriptor(this, key),
          descriptor = {
            configurable: property.configurable,
            enumerable: property.enumerable
          };
      if (property.get)
        descriptor.get = property.get.bind(this);
      if (property.set)
        descriptor.set = property.set.bind(this);
      if ('value' in property) {
        let value = property.value;
        if ('function' === typeof value) {
          descriptor.value = property.value.bind(this);
          descriptor.writable = property.writable;
        } else {
          descriptor.get = Get.bind(this, key);
          descriptor.set = Set.bind(this, key);
        }
      }
      trait[key] = descriptor;
    }
    Object.defineProperty(this, '_publicTrait', { value: trait });
    return this._publicTrait;
  },
  /**
   * Lazy property that holds public API of this object. All the
   * methods and properties that don't start with `"_"` character
   * are considered to be public. All the methods and properties
   * of this property represent proxies to the same named properties
   * of this object. **This is the property must be used to expose
   * this object to the public in a safe manner.**
   * @example
   *
   *    var PointTrait = Trait.compose({
   *      constructor: Point,
   *      _x: 0,
   *      _y: 0,
   *      get magnitude() this._x * this._x + this._y * this._y
   *    }, PublicTrait);
   *    function Point(x, y) Trait.create({}, PointTrait)._public
   */
  get _public() {
    let _public = Trait.create(
      this.constructor ? this.constructor.prototype : {},
      this._publicTrait
    );
    Object.defineProperty(this, '_public', { value: Object.freeze(_public) });
    return this._public;
  }
});
exports.PublicTrait = PublicTrait;