(2) Sprockets' C-style require directives because the people working with ruby don't want to get their hands dirty with crawling the javascript AST and parsing out commonjs or even Harmony-ES module system requires.
(3) Incompatibilities between various JS-focused gems because of sprockets issues. Getting Require.js to work took a long time and then it took a lot longer to get the require.js gem to work with jasmine.js, and even then it ended up being a jerryrigged approach.
In general, sprockets is a mess with respect to Javascript handling versus what you can do in node.js.
(1) Slow
(2) Sprockets' C-style require directives because the people working with ruby don't want to get their hands dirty with crawling the javascript AST and parsing out commonjs or even Harmony-ES module system requires.
(3) Incompatibilities between various JS-focused gems because of sprockets issues. Getting Require.js to work took a long time and then it took a lot longer to get the require.js gem to work with jasmine.js, and even then it ended up being a jerryrigged approach.
In general, sprockets is a mess with respect to Javascript handling versus what you can do in node.js.