let lastTime = 0

let vendors = ['ms', 'moz', 'webkit', 'o']

for (let x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {

  window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame']

  window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] || window[vendors[x] + 'CancelRequestAnimationFrame']

}

if (!window.requestAnimationFrame) {

  window.requestAnimationFrame = function (callback, element) {

    let currTime = new Date().getTime()

    let timeToCall = Math.max(0, 16 - (currTime - lastTime))

    let callbackParams = currTime + timeToCall

    let id = window.setTimeout(() => { callback(callbackParams) }, timeToCall)

    lastTime = currTime + timeToCall

    return id

  }

}

if (!window.cancelAnimationFrame) {

  window.cancelAnimationFrame = function (id) {

    clearTimeout(id)

  }

}

if (!('classList' in document.documentElement)) {

  Object.defineProperty(HTMLElement.prototype, 'classList', {

    get: function () {

      let self = this

      function update (fn) {

        return function (value) {

          let classes = self.className.split(/s+/g)

          let index = classes.indexOf(value)

          fn(classes, index, value)

          self.className = classes.join(' ')

        }

      }

      return {

        add: update(function (classes, index, value) {

          if (!~index) classes.push(value)

        }),

        remove: update(function (classes, index) {

          if (~index) classes.splice(index, 1)

        }),

        toggle: update(function (classes, index, value) {

          if (~index) { classes.splice(index, 1) } else { classes.push(value) }

        }),

        contains: function (value) {

          return !!~self.className.split(/s+/g).indexOf(value)

        },

        item: function (i) {

          return self.className.split(/s+/g)[i] || null

        }

      }

    }

  })

}

if (window.HTMLElement) {

  if (Object.getOwnPropertyNames(HTMLElement.prototype).indexOf('dataset') === -1) {

    Object.defineProperty(HTMLElement.prototype, 'dataset', {

      get: function () {

        let attributes = this.attributes // 获取节点的所有属性

        let name = []

        let value = [] // 定义两个数组保存属性名和属性值

        let obj = {} // 定义一个空对象

        for (let i = 0; i < attributes.length; i++) { // 遍历节点的所有属性

          if (attributes[i].nodeName.slice(0, 5) === 'data-') { // 如果属性名的前面5个字符符合"data-"

            // 取出属性名的"data-"的后面的字符串放入name数组中

            name.push(attributes[i].nodeName.slice(5))

            // 取出对应的属性值放入value数组中

            value.push(attributes[i].nodeValue)

          }

        }

        for (let j = 0; j < name.length; j++) { // 遍历name和value数组

          obj[name[j]] = value[j] // 将属性名和属性值保存到obj中

        }

        return obj // 返回对象

      }

    })

  }

}