I have gotten vertical scrolling by dragging up/down with the mouse to work on my webpage. However, the problem is that it feels pretty abrupt because the scrolling stops instantly when you stop dragging. I would like to add some inertia so that it continues to scroll for a bit after you stop dragging until it comes to a stop.
This is somewhat complicated to implement so I would like some help. This is my all of my current code:
let newScrollY = 0
let element = null
const dragScroll = (enabled) => {
element?.removeEventListener("mousedown", element?.mouseDownFunc, false)
window.removeEventListener("mouseup", element?.mouseUpFunc, false)
window.removeEventListener("mousemove", element?.mouseMoveFunc, false)
element = document.querySelector(".drag")
if (!element || !enabled) return
let lastClientY = 0
let mouseDown = false
element.addEventListener("mousedown", element.mouseDownFunc = (event) => {
event.preventDefault()
mouseDown = true
lastClientY = event.clientY
}, false)
window.addEventListener("mouseup", element.mouseUpFunc = (event) => {
mouseDown = false
}, false)
window.addEventListener("mousemove", element.mouseMoveFunc = (event) => {
if (!mouseDown) return
let scrollElement = element
if (element == document.body) scrollElement = document.documentElement
newScrollY = event.clientY - lastClientY
lastClientY = event.clientY
scrollElement.scrollTop -= newScrollY
}, false)
}
I have figured out a solution. The key was to use the absolute value of the speed and either add/subtract to the scrollTop depending on the sign of the speed (indicating whether they were scrolling up or down).
let newScrollY = 0
let lastScrollTop = 0
let element = null as any
let inertia = false
let mouseDown = false
const dragScroll = (enabled) => {
if (inertia || mouseDown) return
element?.removeEventListener("mousedown", element?.mouseDownFunc, false)
window.removeEventListener("mouseup", element?.mouseUpFunc, false)
window.removeEventListener("mousemove", element?.mouseMoveFunc, false)
element = document.querySelector(".drag")
if (!element || !enabled) return
let lastClientY = 0
mouseDown = false
let time = null
let id = 0
element.addEventListener("mousedown", element.mouseDownFunc = (event) => {
event.preventDefault()
mouseDown = true
inertia = false
time = new Date()
lastClientY = event.clientY
let scrollElement = element
if (element == document.body) scrollElement = document.documentElement
lastScrollTop = scrollElement.scrollTop
cancelAnimationFrame(id)
}, false)
window.addEventListener("mouseup", element.mouseUpFunc = (event) => {
mouseDown = false
const timeDiff = (new Date() as any - time)
let scrollElement = element
if (element == document.body) scrollElement = document.documentElement
let speedY = (scrollElement.scrollTop - lastScrollTop) / timeDiff * 20
let speedYAbsolute = Math.abs(speedY)
const draw = () => {
let scrollElement = element
if (element == document.body) scrollElement = document.documentElement
if (speedYAbsolute > 0) {
if (speedY > 0) {
scrollElement.scrollTop += speedYAbsolute--
} else {
scrollElement.scrollTop -= speedYAbsolute--
}
} else {
inertia = false
}
id = requestAnimationFrame(draw)
}
inertia = true
draw()
}, false)
window.addEventListener("mousemove", element.mouseMoveFunc = (event) => {
if (!mouseDown) return
let scrollElement = element
if (element == document.body) scrollElement = document.documentElement
newScrollY = event.clientY - lastClientY
lastClientY = event.clientY
scrollElement.scrollTop -= newScrollY
}, false)
}