Conflict when simultaneously using keyboard events for scrolling and CSS scroll snapping

Question

You can horizontally scroll my demo page by pressing Space Bar, Page Up / Page Down and Left Arrow / Right Arrow keys. You can also snap scroll with a mouse or trackpad.

But only one or the other works.

Is there a way that keyboard events and CSS scroll snapping can coexist? What am I missing? Any help would be really appreciated, since I’ve been struggling with this problem for over a week.

---

Check out my demo on CodePen

(Please uncomment the relevant piece of CSS code to enable the scroll snapping effect in order to see that keyboard shortcuts stop working.)

---

import animate from "https://cdn.jsdelivr.net/npm/animateplus@2/animateplus.js"

const sections = Array.from(document.querySelectorAll("section")).sort(
  (s1, s2) => {
    return s1.getBoundingClientRect().left - s2.getBoundingClientRect().left
  }
)

const getSectionInView = () => {
  const halfWidth = window.innerWidth / 2
  const index = sections.findIndex(
    section =>
      section.getBoundingClientRect().left <= halfWidth &&
      section.getBoundingClientRect().right > halfWidth
  )
  return index
}

const getNextSection = dir => {
  const sectionInViewIndex = getSectionInView()
  const nextIndex = sectionInViewIndex + dir
  const numSections = sections.length
  const nextSectionIndex =
    nextIndex < 0 || nextIndex >= numSections ? sectionInViewIndex : nextIndex
  return sections[nextSectionIndex]
}

const container = document.scrollingElement

const animateScroll = dir => {
  const from = container.scrollLeft
  const { left } = getNextSection(dir).getBoundingClientRect()
  return progress => (container.scrollLeft = from + progress * left)
}

window.onload = () => {
  document.body.onkeydown = event => {
    switch (event.key) {
      case " ": // Space Bar
      case "PageDown":
      case "ArrowRight": {      
        animate({
          easing: "out-quintic",
          change: animateScroll(1)
        })
        break
      }
      case "PageUp":
      case "ArrowLeft":  {      
        animate({
          easing: "out-quintic",
          change: animateScroll(-1)
        })
        break
      }
    }
  }
}

---

Note: I’m using a small and elegant module called Animate Plus for achieving the smooth scrolling animation.

---

Update: @Kostja’s solution works in Chrome, but not in Safari for Mac or iOS, and it’s crucial to me that it works in Safari.

Answer 1

I guess there is not, the css overwrites the javascript. But you can simply add wheel eventlistener like:

window.addEventListener("wheel", function() {
    if(event.deltaY > 0){
      animate({
        easing: "out-quintic",
        change: animateScroll(1)
      })      
    }
      if(event.deltaY < 0){
      animate({
        easing: "out-quintic",
        change: animateScroll(-1)
      })      
    }      
});

https://codepen.io/kostjaaa/pen/NWWVBKd