Writing Spine = require('spine') in each file is the right way to do.
Yet, there are several possibilities by using the global or window object (browserify sets the global object to window, which is the global namespace):
- in spine.js:
global.Spine = module.exports - in any other .js file bundled by browserify:
global.Spine = require('spine') - in a script tag or an .js file referenced by the .html file, after the spine.js file:
window.Spine = require('spine')