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源码

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>