virtual-scroll-handler

Virtual scrollbar, for when you need to handle scroll events without an actual DOM scrolling.

Usage no npm install needed!

<script type="module">
  import virtualScrollHandler from 'https://cdn.skypack.dev/virtual-scroll-handler';
</script>

README

virtual-scroll-handler

Allows you to handle scroll events in order to trigger and control animations, without having to deal with an actual DOM scrolling. This class creates a virtual scrollbar and is mobile friendly.

See it in action: https://thibautfoussard.com/

Install

npm i virtual-scroll-handler

Hello world

import virtualScrollHandler from 'virtual-scroll-handler'

let scroller = new virtualScrollHandler({
    range: [0, 2000],
    triggers: [{
        y: 1000,
        callback: () => {
            console.log("Callback triggered");
        }
    }]
});

(function loop() {
    requestAnimationFrame(loop);
    scroller.update();
})();

Options

range[min, max]

Min & max deltaY.
A single mouse scroll down event will typically increment the deltaY by 100, so a range from 0 to 2000 implies 20 scroll events to hit the bottom of the virtual scrollbar.

startY

Y starting position within the provided range.
Default is 0.

lerpAmount

Default is .1
For each iteration of the linear interpolation, the amount to interpolate between the mouse position and the camera position. A smaller value will make the animation smoother.
Between 0 and 1.

lerpAmountSwipe: .2

Default is lerpAmount * 4.
Similar to lerpAmount but only affects swipe gestures for mobile devices.

createScrollbar

Boolean. Default is true.
Will add a scrollbar in the DOM, before the closing </body> tag.

customScrollbarStyles

String.
Only active if createScrollbar is set to true.
Adds custom css styles to the DOM.
Note: Instances of virtual-scroll-handler are indexed with unique IDs starting from 0. This ID is referenced in the name of DOM classes and ids.
Example:

const scrollHandler = new virtualScrollHandler({
    range: [0, 1000],
    customScrollbarStyles: `.vsh-scrollbar-0 {  /* <- this is the first instance, so the id is 0 */
            ...
        }`
});

fadeOutDelay

Time in ms after which the scrollbar will fadeout once it has stopped moving. Default is false.

handleSize

Size of the scroll bar handle in percent of the viewport height. Default is .1, since by default, the handle take 10% of the viewport height.

triggers

Array of objects.
This is where you declare when and what is going to happen.
Each trigger is an object made of these options:

y

The deltaY value which will trigger the action when reached.

condition

Default is >y, meaning that the callback is triggered when the current virtual scroll position is above the y trigger value.

callback

The callback function to trigger.

once

Default is false.
If set to true, the callback function will only be triggered once.

Properties

.completion

Returns a number between 0 and 1.

let scroller = new scrollHandler({
    range: [0, 2000]
});

console.log(scroller.completion);

active

Default is true.
If set to false, the scroll is disabled.

domElements

An object containing:
.scrollbar: the DOM element of the whole scrollbar and its children
.handle: the part of the scrollbar that moves vertically

scroller.domElements.scrollbar.style.opacity = 0;

Methods

goTo( distance: number, animated: bool)

Scroll to a point in the range of the scroller.
The 'animated' parameter makes the scroll instant or animated. Default is true.

scroller.goTo( 500, false );

Example

import scrollHandler from 'virtual-scroll-handler'

new scrollHandler({
    range: [0, 2000],
    startY: 0,
    triggers: [{
        y: 1000,
        condition: '<y',
        callback: () => {
            console.log("Callback triggered");
        },
        once: true
    }],
    createScrollbar: true,
    customScrollbarStyles: `.vsh-scrollbar { mix-blend-mode: difference; }`,
    fadeOutDelay: 500
});

(function loop() {
    requestAnimationFrame(loop);
    scroller.update();
    console.log(scroller.completion);
})();