<template>
 <div id="nav">
 <router-link to="/">Home</router-link> |
 <router-link to="/about">About</router-link>
 </div>
 <count-to :startVal="0" :endVal="2045" :duration="4000"></count-to>
 <router-view/>
</template>

let lastTime = 0
const prefixes = 'webkit moz ms o'.split(' ') // 各浏览器前缀

let requestAnimationFrame
let cancelAnimationFrame

const isServer = typeof window === 'undefined'
if (isServer) {
 requestAnimationFrame = function () {
 }
 cancelAnimationFrame = function () {
 }
} else {
 requestAnimationFrame = window.requestAnimationFrame
 cancelAnimationFrame = window.cancelAnimationFrame
 let prefix
 // 通过遍历各浏览器前缀，来得到requestAnimationFrame和cancelAnimationFrame在当前浏览器的实现形式
 for (let i = 0; i < prefixes.length; i++) {
 if (requestAnimationFrame && cancelAnimationFrame) { break }
 prefix = prefixes[i]
 requestAnimationFrame = requestAnimationFrame || window[prefix + 'RequestAnimationFrame']
 cancelAnimationFrame = cancelAnimationFrame || window[prefix + 'CancelAnimationFrame'] || window[prefix + 'CancelRequestAnimationFrame']
 }

 // 如果当前浏览器不支持requestAnimationFrame和cancelAnimationFrame，则会退到setTimeout
 if (!requestAnimationFrame || !cancelAnimationFrame) {
 requestAnimationFrame = function (callback) {
 const currTime = new Date().getTime()
 // 为了使setTimteout的尽可能的接近每秒60帧的效果
 const timeToCall = Math.max(0, 16 - (currTime - lastTime))
 const id = window.setTimeout(() => {
 const time = currTime + timeToCall
 callback(time)
 }, timeToCall)
 lastTime = currTime + timeToCall
 return id
 }

 cancelAnimationFrame = function (id) {
 window.clearTimeout(id)
 }
 }
}

export { requestAnimationFrame, cancelAnimationFrame }

<template>
 <span>
 {{displayValue}}
 </span>
</template>
<script>
import { requestAnimationFrame, cancelAnimationFrame } from './requestAnimationFrame.js'
export default {
 props: {
 startVal: {
 type: Number,
 required: false,
 default: 0
 },
 endVal: {
 type: Number,
 required: false,
 default: 2017
 },
 duration: {
 type: Number,
 required: false,
 default: 3000
 },
 autoplay: {
 type: Boolean,
 required: false,
 default: true
 },
 decimals: {
 type: Number,
 required: false,
 default: 0,
 validator (value) {
 return value >= 0
 }
 },
 decimal: {
 type: String,
 required: false,
 default: '.'
 },
 separator: {
 type: String,
 required: false,
 default: ','
 },
 prefix: {
 type: String,
 required: false,
 default: ''
 },
 suffix: {
 type: String,
 required: false,
 default: ''
 },
 useEasing: {
 type: Boolean,
 required: false,
 default: true
 },
 easingFn: {
 type: Function,
 default (t, b, c, d) {
 return c * (-Math.pow(2, -10 * t / d) + 1) * 1024 / 1023 + b
 }
 }
 },
 data () {
 return {
 localStartVal: this.startVal,
 displayValue: this.formatNumber(this.startVal),
 printVal: null,
 paused: false,
 localDuration: this.duration,
 startTime: null,
 timestamp: null,
 remaining: null,
 rAF: null
 }
 },
 computed: {
 countDown () {
 return this.startVal > this.endVal
 }
 },
 watch: {
 startVal () {
 if (this.autoplay) {
 this.start()
 }
 },
 endVal () {
 if (this.autoplay) {
 this.start()
 }
 }
 },
 mounted () {
 if (this.autoplay) {
 this.start()
 }
 this.$emit('mountedCallback')
 },
 methods: {
 start () {
 this.localStartVal = this.startVal
 this.startTime = null
 this.localDuration = this.duration
 this.paused = false
 this.rAF = requestAnimationFrame(this.count)
 },
 pauseResume () {
 if (this.paused) {
 this.resume()
 this.paused = false
 } else {
 this.pause()
 this.paused = true
 }
 },
 pause () {
 cancelAnimationFrame(this.rAF)
 },
 resume () {
 this.startTime = null
 this.localDuration = +this.remaining
 this.localStartVal = +this.printVal
 requestAnimationFrame(this.count)
 },
 reset () {
 this.startTime = null
 cancelAnimationFrame(this.rAF)
 this.displayValue = this.formatNumber(this.startVal)
 },
 count (timestamp) {
 if (!this.startTime) this.startTime = timestamp
 this.timestamp = timestamp
 const progress = timestamp - this.startTime
 this.remaining = this.localDuration - progress

 if (this.useEasing) {
 if (this.countDown) {
 this.printVal = this.localStartVal - this.easingFn(progress, 0, this.localStartVal - this.endVal, this.localDuration)
 } else {
 this.printVal = this.easingFn(progress, this.localStartVal, this.endVal - this.localStartVal, this.localDuration)
 }
 } else {
 if (this.countDown) {
 this.printVal = this.localStartVal - ((this.localStartVal - this.endVal) * (progress / this.localDuration))
 } else {
 this.printVal = this.localStartVal + (this.endVal - this.localStartVal) * (progress / this.localDuration)
 }
 }
 if (this.countDown) {
 this.printVal = this.printVal < this.endVal ? this.endVal : this.printVal
 } else {
 this.printVal = this.printVal > this.endVal ? this.endVal : this.printVal
 }

 this.displayValue = this.formatNumber(this.printVal)
 if (progress < this.localDuration) {
 this.rAF = requestAnimationFrame(this.count)
 } else {
 this.$emit('callback')
 }
 },
 isNumber (val) {
 return !isNaN(parseFloat(val))
 },
 formatNumber (num) {
 num = num.toFixed(this.decimals)
 num += ''
 const x = num.split('.')
 let x1 = x[0]
 const x2 = x.length > 1 ? this.decimal + x[1] : ''
 const rgx = /(\d+)(\d{3})/
 if (this.separator && !this.isNumber(this.separator)) {
 while (rgx.test(x1)) {
 x1 = x1.replace(rgx, '$1' + this.separator + '$2')
 }
 }
 return this.prefix + x1 + x2 + this.suffix
 }
 },
 unmounted () {
 cancelAnimationFrame(this.rAF)
 }
}
</script>