@airyrooms/catela/util/scrollToAnimation.js

let scrollToY = function () {}
try {
  // first add raf shim
  // http://www.paulirish.com/2011/requestanimationframe-for-smart-animating/
  window.requestAnimFrame = (function () {
    return window.requestAnimationFrame ||
            window.webkitRequestAnimationFrame ||
            window.mozRequestAnimationFrame ||
            function (callback) {
              window.setTimeout(callback, 1000 / 60)
            }
  })()

  // main function
  scrollToY = function scrollToY (scrollTargetY, speed, easing) {
    // scrollTargetY: the target scrollY property of the window
    // speed: time in pixels per second
    // easing: easing equation to use

    var scrollY = window.scrollY,
        scrollTargetY = scrollTargetY || 0,
        speed = speed || 2000,
        easing = easing || 'easeOutSine',
        currentTime = 0

    // min time .1, max time .8 seconds
    var time = Math.max(0.1, Math.min(Math.abs(scrollY - scrollTargetY) / speed, 0.8))

    // easing equations from https://github.com/danro/easing-js/blob/master/easing.js
    var PI_D2 = Math.PI / 2,
        easingEquations = {
          easeOutSine: function (pos) {
            return Math.sin(pos * (Math.PI / 2))
          },
          easeInOutSine: function (pos) {
            return (-0.5 * (Math.cos(Math.PI * pos) - 1))
          },
          easeInOutQuint: function (pos) {
            if ((pos /= 0.5) < 1) {
              return 0.5 * Math.pow(pos, 5)
            }
            return 0.5 * (Math.pow((pos - 2), 5) + 2)
          }
        }

      // add animation loop
    function tick () {
      currentTime += 1 / 60

      var p = currentTime / time
      var t = easingEquations[easing](p)

      if (p < 1) {
        window.requestAnimFrame(tick)
        window.scrollTo(0, scrollY + ((scrollTargetY - scrollY) * t))
      } else {
        window.scrollTo(0, scrollTargetY)
      }
    }

    tick()
  }
} catch (err) { /* Suppressing */ }

export default {
  scrollToY: scrollToY
}