About Cocos2d-x
Started in 2010, Cocos2d-x is an open source, cross-platform game engine. It is loaded with powerful features that allow developers to create spectacular games with ease.Using the most recent version of Cocos2D-x you can target Windows, Mac, Linux, iOS and Android.Cocos2d-x framework using C++ language for development.
What is Cocos2d-js ?
Cocos2d-js is game engine port of Cocos2d-x.its targeted web and native games. It's mean its fully cross platform . you can develop HTML5 2d games and native games.Cocos2d-js  using for language  Javascript. Because of this .It can be run browser and native platforms. Even so Cocos2d-js dont losing any power of C++. Because cocos2d-js sources compile to C++ then works like Cocos2d-x games.
Main Features ( I take from Cocos2d-x websites)
- Support All modern browsers and native platforms
 - Scene management (workflow)
 - Transitions between scenes
 - Sprites and Sprite Sheets
 - Effects: Lens, Ripple, Waves, Liquid, etc.
 - Actions (behaviours):
- Trasformation Actions: Move, Rotate, Scale, Fade, Tint, etc.
 - Composable actions: Sequence, Spawn, Repeat, Reverse
 - Ease Actions: Exp, Sin, Cubic, Elastic, etc.
 - Misc actions: CallFunc, OrbitCamera, Follow, Tween
 
 - Assets manager (hot update)
 - Basic menus and buttons
 - Integrated with physics engines: Chipmunk and Box2d
 - Particle system
 - Skeleton Animations: Spine and Armature support
 - Fonts:
- Fast font rendering using Fixed and Variable width fonts
 - Support for .ttf fonts
 
 - Tile Map support: Orthogonal, Isometric and Hexagonal
 - Parallax scrolling
 - Motion Streak
 - Render To Texture
 - Touch/Accelerometer on mobile devices
 - Touch/Mouse/Keyboard on desktop
 - Sound Engine support (CocosDenshion library) based on OpenAL or WebAudio on web
 - Integrated Slow motion/Fast forward
 - Fast and compressed textures: PVR compressed and uncompressed textures, ETC1 compressed textures, and more
 - Resolution Independence
 - Modularized engine for customization
 - Open Source Commercial Friendly: Compatible with open and closed source projects
 - OpenGL ES 2.0 (mobile) / OpenGL 2.1 (desktop) based
 - Full WebGL support and auto canvas fallback
 
After this post. I will continue blogging about Cocos2d-js . You can add my blog to your bookmarks. :)