[cocos2d-x从c++到js]04：javascript中的继承
对于面向对象语言来说，继承机制是代码复用的基础，很不幸的是javascript作为一个基于原型继承的语言，并没有在本身语言层面上直接作出对类继承的支持。
但是js语言拥有很强大的表现力。所以一般是js的使用者自行设计一套继承机制，这个机制必须包括几个点，对私有访问权限的模拟，对属性和类属性的不同实现，对方法覆盖的支持，对父类被覆盖方法的访问等。
cocos2d-x中，整合了两套继承机制，看《MoonWarriors》例子中的源码SysMenu.js文件
var SysMenu = cc.Layer.extend({
_ship:null,
ctor:function () {
cc.associateWithNative( this, cc.Layer );
},
init:function () {
var bRet = false;
if (this._super()) {
winSize = cc.Director.getInstance().getWinSize();
var sp = cc.Sprite.create(s_loading);
sp.setAnchorPoint(cc.p(0,0));
this.addChild(sp, 0, 1);
var logo = cc.Sprite.create(s_logo);
logo.setAnchorPoint(cc.p(0, 0));
logo.setPosition(0, 250);
this.addChild(logo, 10, 1);
var newGameNormal = cc.Sprite.create(s_menu, cc.rect(0, 0, 126, 33));
var newGameSelected = cc.Sprite.create(s_menu, cc.rect(0, 33, 126, 33));
var newGameDisabled = cc.Sprite.create(s_menu, cc.rect(0, 33 * 2, 126, 33));
var gameSettingsNormal = cc.Sprite.create(s_menu, cc.rect(126, 0, 126, 33));
var gameSettingsSelected = cc.Sprite.create(s_menu, cc.rect(126, 33, 126, 33));
var gameSettingsDisabled = cc.Sprite.create(s_menu, cc.rect(126, 33 * 2, 126, 33));
var aboutNormal = cc.Sprite.create(s_menu, cc.rect(252, 0, 126, 33));
var aboutSelected = cc.Sprite.create(s_menu, cc.rect(252, 33, 126, 33));
var aboutDisabled = cc.Sprite.create(s_menu, cc.rect(252, 33 * 2, 126, 33));
var newGame = cc.MenuItemSprite.create(newGameNormal, newGameSelected, newGameDisabled, function () {
this.onButtonEffect();
flareEffect(this, this, this.onNewGame);
}.bind(this));
var gameSettings = cc.MenuItemSprite.create(gameSettingsNormal, gameSettingsSelected, gameSettingsDisabled, this.onSettings, this);
var about = cc.MenuItemSprite.create(aboutNormal, aboutSelected, aboutDisabled, this.onAbout, this);
var menu = cc.Menu.create(newGame, gameSettings, about);
menu.alignItemsVerticallyWithPadding(10);
this.addChild(menu, 1, 2);
menu.setPosition(winSize.width / 2, winSize.height / 2 - 80);
this.schedule(this.update, 0.1);
var tmp = cc.TextureCache.getInstance().addImage(s_ship01);
this._ship = cc.Sprite.createWithTexture(tmp,cc.rect(0, 45, 60, 38));
this.addChild(this._ship, 0, 4);
var pos = cc.p(Math.random() * winSize.width, 0);
this._ship.setPosition( pos );
this._ship.runAction(cc.MoveBy.create(2, cc.p(Math.random() * winSize.width, pos.y + winSize.height + 100)));
if (MW.SOUND) {
cc.AudioEngine.getInstance().setMusicVolume(0.7);
cc.AudioEngine.getInstance().playMusic(s_mainMainMusic, true);
}
bRet = true;
}
return bRet;
},
onNewGame:function (pSender) {
var scene = cc.Scene.create();
scene.addChild(GameLayer.create());
scene.addChild(GameControlMenu.create());
cc.Director.getInstance().replaceScene(cc.TransitionFade.create(1.2, scene));
},
onSettings:function (pSender) {
this.onButtonEffect();
var scene = cc.Scene.create();
scene.addChild(SettingsLayer.create());
cc.Director.getInstance().replaceScene(cc.TransitionFade.create(1.2, scene));
},
onAbout:function (pSender) {
this.onButtonEffect();
var scene = cc.Scene.create();
scene.addChild(AboutLayer.create());
cc.Director.getInstance().replaceScene(cc.TransitionFade.create(1.2, scene));
},
update:function () {
if (this._ship.getPosition().y > 480) {
var pos = cc.p(Math.random() * winSize.width, 10);
this._ship.setPosition( pos );
this._ship.runAction( cc.MoveBy.create(
parseInt(5 * Math.random(), 10),
cc.p(Math.random() * winSize.width, pos.y + 480)));
}
},
onButtonEffect:function(){
if (MW.SOUND) {
var s = cc.AudioEngine.getInstance().playEffect(s_buttonEffect);
