code: function onComplete (err) {
      if (err) {
        console.log('interpolation encountered an error: ', err)
        return callback(err)
      }
      // set is complete and create a queue drain function
      // however, a feed may not have any interpolated times, so
      // `isComplete` is set in case nothing is pushed to the queue
      isComplete = true
      updateQueue.drain = () => {
        console.log('interpolation completed successfully')
        callback(err)
      }
    }
docs: Helper function to call upon completion of interpolation