实现数字从0增长，每帧增长1的速度，直到100

 let startValue = 0;
 let endValue = 100
 let request = null
 function animate () {
   startValue += 1
   console.log(startValue)
   if (startValue >= endValue) {
     cancelAnimationFrame(request)
   } else {
     request = requestAnimationFrame(animate)
   }
 }

实现数字从0增长，匀速在2s内增加到100 （每秒50）

 let startValue = 0
 let endValue = 100
 let request = null
 let starttime = new Date().getTime()
 const duration = 2000
 function animate () {
   var timestamp = new Date().getTime()
   var runtime = timestamp - starttime
   var progress = runtime / duration
   progress = Math.min(progress, 1)
   startValue = (endValue * progress)
   console.log(startValue)
   if (runtime < duration) { // if duration not met yet
     requestAnimationFrame(animate)
   } else {
     cancelAnimationFrame(request)
   }
 }
 requestAnimationFrame(animate)

实现数字从0增长，按一定函数在2s内增加到100

 const duration = 2000
 let startValue = 0
 let request = null
 let starttime = new Date().getTime()
 let endValue = 100
 // cancelAnimationFrame(request)
 const animate = () => {
   request = window.requestAnimationFrame(animate)
   draw()
 }
 const draw = (timestamp = new Date().getTime()) => {
   const Linear = k => k
   const QuadraticIn = k => k * k
   const QuadraticOut = k => k * (2 - k)
   const CubicInOut = k => {
     if ((k *= 2) < 1) {
       return 0.5 * k * k * k
     }
     return 0.5 * ((k -= 2) * k * k + 2)
   }
   var runtime = timestamp - starttime
   var progress = runtime / duration
   progress = Math.min(progress, 1)
   startValue = CubicInOut(progress) * endValue
   console.log(startValue)
   if (startValue >= endValue) {
     cancelAnimationFrame(request)
   }
 }
 animate()