项目场景：
数据可视化大屏开发的过程中，需要实现一种滚动数字的效果，在使用vue2时，使用vue-count-to完全没有问题，功能也比较完善(滚动时长，开始值，结束值，前缀，后缀，千分隔符，小数分隔符等等)，但是在vue3中使用会出现问题。
<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>
展示的效果
问题描述：
出现的错误时 == Cannot read property ‘_c’ of undefined== 这是一个_c的属性没有找到，具体的情况也不是很清楚。在vue-count-to打包后的源码中可以大致看出来，这是在render函数中出现的错误。但是还是没法下手。
解决方案：
采用的方法是直接复制node_modules下vue-count-to的源文件（src下），到自己项目的components下。如图
然后根据eslint的检查，修改代码，直到不报错，且记删除package.json下刚刚引入的vue-count-to的依赖。如图
最后重启项目。
vue-count-to组件 vue3使用
vue-count-to源码，vue3修改
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>