code: function throttled (fn, delay) {
    let lastCall = 0
    return function (...args) {
      const now = new Date().getTime()
      if (now - lastCall < delay) {
        return
      }
      lastCall = now
      return fn(...args)
    }
  }
docs: Creates a throttled function that only invokes func at most
  once per every wait milliseconds.
  @name throttled
  @param  {Function} fn   Function to debounce
  @param  {Number} delay  How long to wait
  @return {Function}      Executed Function