you might write a lot of game files, you can specify in cocos2d.js file, which is much easier to write your own
tags in html, there are tens of dozens js file for game engine alone.
game file (??? kb) + engine file (200kb)\\ +\\ box2d\\ ,\\ which\\ is\\ pretty\\ big\\ to\\ download\\ over\\ the\\ internet.
your\\ web\\ page\\ will\\ lockup\\ downloading\\ the\\ js\\ files,\\ which\\ is\\ bad\\ for\\ user\\ experience.
by\\ having\\ cocos2d.js\\ which\\ is
1-2kb, you wont add too much weight to page loading. and when page loading is done, it then begins downloading the game.