This is a pretty clean way to run sync and async tasks using Promise and a reducer func

task_runner.js

module.exports = run

// Run tasks in sequence or async can be done in a very expressive way using
// Promise and a reducer
function run(tasks) {
  return tasks.reduce(
    (acc, task) => acc.then(lastResult => {
      if (typeof task === 'function') {
        // A task is a function that takes a result from a previous task and returns
        // a promise executor function
        return new Promise(task(lastResult))
      } else {
        // If it's an array of tasks, each task is run asyncronously
        // and continues after all async task if finished
        return Promise.all(task.map(t => new Promise(t(lastResult))))
      }
    }), Promise.resolve()
  )
}