code: function invoker (app) {
    return function invoker__ (name, fn, options) {
      if (app.isRegistered(name)) {
        return
      }
  
      var ret = tryCatch(fn, {
        return: true,
        context: app.isBase ? app : null,
        args: app.isBase ? [app, app.base, options, app.env] : [app, options]
      })
  
      if (ret instanceof Error) {
        ret._pluginName = name
        app.emit('error', ret)
      }
    }
  }
docs: Utils