lib/plugin-templates.js
function engine(path, options, fn) {
  options.filename = path;

  fs.readFile(path, 'utf8', function (err, str) {
    if (err) return fn(err);
    engine.render(str, options, fn);
  });
}
function engine(path, options, fn) {
  options.filename = path;

  fs.readFile(path, 'utf8', function (err, str) {
    if (err) return fn(err);
    engine.render(str, options, fn);
  });
}
Express 3 Template Engine