Capistrano 3 How to write correctly a local task?

In my nodjs/a,gular2 project, I am trying to run locally the build-sot process as a local task, before deploying it , but I cannot get it right , how can I set it :

task :build_production_aot do
  run_locally do
    set :local_app_path, Dir.pwd
    set :local_client_path, "#{fetch(:local_app_path)}/client"
    sh 'npm run build:prod-aot'
  end
end

thanks for feedback

via erwin