init.pp

class myapp (){
  file { '/opt/serverapp':
    ensure => 'directory',
    owner => 'myuser',
    group => 'myuser'
  }
  
  nodejs::npm { 'express from the npm registry':
    ensure  => 'present',
    package => 'express',
    target  => '/opt/packages',
  }
  
  nodejs::npm { 'serverapp':
    ensure           => 'present',
    target           => '/opt/serverapp',
    use_package_json => true,
  }
}