Try this JS solution that toggles webkitOverflowScrolling style. The trick here is that this style is off, mobile Safari goes to ordinary scrolling and prevents over-bounce — alas, it is not able to cancel ongoing drag. This complex solution also tracks onscroll as bounce over the top makes scrollTop negative that may be tracked. This solution was tested on iOS 12.1.1 and has single drawback: while accelerating the scroll single over-bounce still happens as resetting the style may not cancel it immediately.
function preventScrollVerticalBounceEffect(container) {
setTouchScroll(true) //!: enable before the first scroll attempt
container.addEventListener("touchstart", onTouchStart)
container.addEventListener("touchmove", onTouch, { passive: false })
container.addEventListener("touchend", onTouchEnd)
container.addEventListener("scroll", onScroll)
function isTouchScroll() {
return !!container.style.webkitOverflowScrolling
}
let prevScrollTop = 0, prevTouchY, opid = 0
function setTouchScroll(on) {
container.style.webkitOverflowScrolling = on ? "touch" : null
//Hint: auto-enabling after a small pause makes the start
// smoothly accelerated as required. After the pause the
// scroll position is settled, and there is no delta to
// make over-bounce by dragging the finger. But still,
// accelerated content makes short single over-bounce
// as acceleration may not be off instantly.
const xopid = ++opid
!on && setTimeout(() => (xopid === opid) && setTouchScroll(true), 250)
if(!on && container.scrollTop < 16)
container.scrollTop = 0
prevScrollTop = container.scrollTop
}
function isBounceOverTop() {
const dY = container.scrollTop - prevScrollTop
return dY < 0 && container.scrollTop < 16
}
function isBounceOverBottom(touchY) {
const dY = touchY - prevTouchY
//Hint: trying to bounce over the bottom, the finger moves
// up the screen, thus Y becomes smaller. We prevent this.
return dY < 0 && container.scrollHeight - 16 <=
container.scrollTop + container.offsetHeight
}
function onTouchStart(e) {
prevTouchY = e.touches[0].pageY
}
function onTouch(e) {
const touchY = e.touches[0].pageY
if(isBounceOverBottom(touchY)) {
if(isTouchScroll())
setTouchScroll(false)
e.preventDefault()
}
prevTouchY = touchY
}
function onTouchEnd() {
prevTouchY = undefined
}
function onScroll() {
if(isTouchScroll() && isBounceOverTop()) {
setTouchScroll(false)
}
}
}