text: /* @flow */
  
  import { isDef, isUndef } from 'shared/util'
  import { updateListeners } from 'core/vdom/helpers/index'
  import { isIE, supportsPassive, isUsingMicroTask } from 'core/util/index'
  import { RANGE_TOKEN, CHECKBOX_RADIO_TOKEN } from 'web/compiler/directives/model'
  import { currentFlushTimestamp } from 'core/observer/scheduler'
  
  // normalize v-model event tokens that can only be determined at runtime.
  // it's important to place the event as the first in the array because
  // the whole point is ensuring the v-model callback gets called before
  // user-attached handlers.
  function normalizeEvents (on) {
    /* istanbul ignore if */
    if (isDef(on[RANGE_TOKEN])) {
      // IE input[type=range] only supports `change` event
      const event = isIE ? 'change' : 'input'
      on[event] = [].concat(on[RANGE_TOKEN], on[event] || [])
      delete on[RANGE_TOKEN]
    }
    // This was originally intended to fix #4521 but no longer necessary
    // after 2.5. Keeping it for backwards compat with generated code from < 2.4
    /* istanbul ignore if */
    if (isDef(on[CHECKBOX_RADIO_TOKEN])) {
      on.change = [].concat(on[CHECKBOX_RADIO_TOKEN], on.change || [])
      delete on[CHECKBOX_RADIO_TOKEN]
    }
  }
  
  let target: any
  
  function createOnceHandler (event, handler, capture) {
    const _target = target // save current target element in closure
    return function onceHandler () {
      const res = handler.apply(null, arguments)
      if (res !== null) {
        remove(event, onceHandler, capture, _target)
      }
    }
  }
  
  function add (
    name: string,
    handler: Function,
    capture: boolean,
    passive: boolean
  ) {
    // async edge case #6566: inner click event triggers patch, event handler
    // attached to outer element during patch, and triggered again. This
    // happens because browsers fire microtask ticks between event propagation.
    // the solution is simple: we save the timestamp when a handler is attached,
    // and the handler would only fire if the event passed to it was fired
    // AFTER it was attached.
    if (isUsingMicroTask) {
      const attachedTimestamp = currentFlushTimestamp
      const original = handler
      handler = original._wrapper = function (e) {
        if (e.timeStamp >= attachedTimestamp) {
          return original.apply(this, arguments)
        }
      }
    }
    target.addEventListener(
      name,
      handler,
      supportsPassive
        ? { capture, passive }
        : capture
    )
  }
  
  function remove (
    name: string,
    handler: Function,
    capture: boolean,
    _target?: HTMLElement
  ) {
    (_target || target).removeEventListener(
      name,
      handler._wrapper || handler,
      capture
    )
  }
  
  function updateDOMListeners (oldVnode: VNodeWithData, vnode: VNodeWithData) {
    if (isUndef(oldVnode.data.on) && isUndef(vnode.data.on)) {
      return
    }
    const on = vnode.data.on || {}
    const oldOn = oldVnode.data.on || {}
    target = vnode.elm
    normalizeEvents(on)
    updateListeners(on, oldOn, add, remove, createOnceHandler, vnode.context)
    target = undefined
  }
  
  export default {
    create: updateDOMListeners,
    update: updateDOMListeners
  }
  