wrappy.js

// Returns a wrapper function that returns a wrapped callback
// The wrapper function should do some stuff, and return a
// presumably different callback function.
// This makes sure that own properties are retained, so that
// decorations and such are not lost along the way.
module.exports = wrappy
function wrappy (fn, cb) {
  if (fn && cb) return wrappy(fn)(cb)

  if (typeof fn !== 'function')
    throw new TypeError('need wrapper function')

  Object.keys(fn).forEach(function (k) {
    wrapper[k] = fn[k]
  })

  return wrapper

  function wrapper() {
    var args = new Array(arguments.length)
    for (var i = 0; i < args.length; i++) {
      args[i] = arguments[i]
    }
    var ret = fn.apply(this, args)
    var cb = args[args.length-1]
    if (typeof ret === 'function' && ret !== cb) {
      Object.keys(cb).forEach(function (k) {
        ret[k] = cb[k]
      })
    }
    return ret
  }
}