Math.easeInOutQuad = function(t, b, c, d) {
  t /= d / 2
  if (t < 1) {
    return c / 2 * t * t + b
  }
  t--
  return -c / 2 * (t * (t - 2) - 1) + b
}
 
var requestAnimFrame = (function() {
  return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function(callback) { window.setTimeout(callback, 1000 / 60) }
})()
 
/**
 * @param {number} amount
 */
function move(amount) {
  document.documentElement.scrollTop = amount
  document.body.parentNode.scrollTop = amount
  document.body.scrollTop = amount
}
 
function position() {
  return document.documentElement.scrollTop || document.body.parentNode.scrollTop || document.body.scrollTop
}
 
/**
 * @param {number} to
 * @param {number} duration
 * @param {Function} callback
 */
export function scrollTo(to, duration, callback) {
  const start = position()
  const change = to - start
  const increment = 20
  let currentTime = 0
  duration = (typeof (duration) === 'undefined') ? 500 : duration
  var animateScroll = function() {
    // increment the time
    currentTime += increment
    // find the value with the quadratic in-out easing function
    var val = Math.easeInOutQuad(currentTime, start, change, duration)
    // move the document.body
    move(val)
    // do the animation unless its over
    if (currentTime < duration) {
      requestAnimFrame(animateScroll)
    } else {
      if (callback && typeof (callback) === 'function') {
        // the animation is done so lets callback
        callback()
      }
    }
  }
  animateScroll()
}

import { scrollTo } from './scroll.js';
 
export default {
  methods: {
    smoothScroll() {
      scrollTo(0, 1000, () => {
        console.log('滾動結束！');
      });
    }
  },
};

<template>
  <div>
    <button @click="smoothScroll">平滑滾動到頂部</button>
  </div>
</template>