WebAssets Filter to compile ES6 to ES5 using DukPY and BabelJS

babelfilter.py

# -*- coding: utf-8 -*-
from __future__ import absolute_import, print_function
from webassets.filter import Filter


__all__ = ('BabelJS',)

# NOTE: When using the BabelJS compiler for code 
# that needs to run in the browser make sure to add 
# https://cdnjs.cloudflare.com/ajax/libs/babel-core/4.6.6/browser-polyfill.js

class BabelJS(Filter):
    """WebAssets filter to compile ES6 to ES5 using DukPY.
    
    can be registered in WebAssets using::
    
        import webassets.filter
        webassets.filter.register_filter(BabelJS)
        
    it will be available as ``babeljs``
    """
    name = 'babeljs'
    max_debug_level = None

    def setup(self):
        try:
            import dukpy
        except ImportError:
            raise EnvironmentError('The "dukpy" package is not installed.')
        else:
            self.dukpy = dukpy
        super(BabelJS, self).setup()

    def input(self, _in, out, **kw):
        src = self.dukpy.babel_compile(_in.read())
        out.write(src)