Running Node app through Grunt

I am trying to run my Node application as a Grunt task. I need to spawn this as a child process, however, to allow me to run the watch task in parallel.

This works:

grunt.registerTask('start', function () {
  grunt.util.spawn(
    { cmd: 'node'
    , args: ['app.js']
    })

  grunt.task.run('watch:app')
})

However, when changes are detected by the watch task, this will trigger the start task again. Before I spawn another child process of my Node app, I need to kill the previous one.

I can't figure out how to kill the process, however. Something like this does not work:

var child

grunt.registerTask('start', function () {
  if (child) child.kill()
  child = grunt.util.spawn(
    { cmd: 'node'
    , args: ['app.js']
    })

  grunt.task.run('watch:app')
})

It appears that:

1. Even though I store the spawned process in a variable outside of the function context, it does not persist, so the next time the start task is run, child is undefined.
2. child has no kill function…