A most basic generator runner

runner.js

function run (iterator) {

  // Kick off the promise chain
  Promise.resolve().then(
    function resolved (value) {

      // Get the next yielded iterator step,
      // passing in the value from the last
      // fulfillment
      const next = iterator.next(value)

      // If done, return
      if (next.done) return

      // Cast the next value to a promise
      Promise.resolve(next.value).then(

        // If resolved, recursively go to
        // the next step
        resolved, 

        // If rejected, throw the reason back
        // to the iterator so that it can get
        // catched there
        reason => {
          iterator.throw(reason)
        }
      )
    }
  )
}