JSTransform require.extension to auto-magically convert ES6 to ES5 during runtime.

jstransform-require.js

var fs          = require('fs');
var jstransform = require('jstransform');
var path        = require('path');
var js          = require.extensions['.js'];

module.exports = function(visitors) {
  visitors = visitors.reduce(function(visitors, visitor) {
    return visitors.concat(visitor.visitorList);
  }, []);

  require.extensions['.js'] = function(module, filename) {
    if (filename.match(/node_modules/)) {
      return js(module, filename);
    }

    var before    = fs.readFileSync(filename, 'utf8');
    var after     = jstransform.transform(visitors, before).code;

    return module._compile(after, filename);
  };
};

server.js

require('./lib/jstransform-require')([
  require('jstransform/visitors/es6-arrow-function-visitors'),
  require('jstransform/visitors/es6-class-visitors'),
  require('jstransform/visitors/es6-destructuring-visitors'),
  require('jstransform/visitors/es6-object-short-notation-visitors'),
  require('jstransform/visitors/es6-rest-param-visitors'),
  require('jstransform/visitors/es7-spread-property-visitors'),
  require('jstransform/visitors/es6-template-visitors'),
]);

var debug = require('debug')('app');
var app = require('./app');

app.set('port', process.env.PORT || 3000);

var server = app.listen(app.get('port'), function() {
  debug('Express server listening on port ' + server.address().port);
});

$ DEBUG=app NODE_ENV=development node --harmony server/server.js 
  app Express server listening on port 3000 +0ms
GET /parallel3 304 3019ms

Aw yeah, that's awesome.