virtual-scroll

A 2kb gzipped low-level library to create custom scrollers with touch and keyboard support. This is heavily inspired by Bartek Drozdz VirtualScroll util. See his article for reference.

Features

• Can create multiple instances with different elements as targets
• Let you do the actual scrolling logic: use CSS Transforms, WebGL animation or anything you like
• Native arrow keys support and shift/space support mimicking default browser behaviour

For high-level libraries based off virtual-scroll, check locomotive-scroll or smooth-scrolling.

Installation

npm i virtual-scroll -S

Usage & API

Constructor

• new VirtualScroll(options)
  • el: the target element for mobile touch events. Defaults to window.
  • mouseMultiplier: General multiplier for all mousewheel (including Firefox). Default to 1.
  • touchMultiplier: Mutiply the touch action by this modifier to make scroll faster than finger movement. Defaults to 2.
  • firefoxMultiplier: Firefox on Windows needs a boost, since scrolling is very slow. Defaults to 15.
  • keyStep: How many pixels to move with each key press. Defaults to 120.
  • preventTouch: If true, automatically call e.preventDefault on touchMove. Defaults to false.
  • unpreventTouchClass: Elements with this class won't preventDefault on touchMove. For instance, useful for a scrolling text inside a VirtualScroll-controled element. Defaults to vs-touchmove-allowed.
  • passive: if used, will use passive events declaration for the wheel and touch listeners. Can be true or false. Defaults to undefined.
  • useKeyboard: if true, allows to use arrows to navigate, and space to jump from one screen. Defaults to true
  • useTouch: if true, uses touch events to simulate scrolling. Defaults to true

Methods

• instance.on(callback, context) Listen to the scroll event using the specified callback and optional context.

• instance.off(callback, context) Remove the listener.

• instance.destroy() Remove all events and unbind the DOM listeners.

Events note: Each instance will listen only once to any DOM listener. These listener are enabled/disabled automatically. However, it's a good practice to always call destroy() on your VirtualScroll instance, especially if you are working with a SPA.

Event

When a scroll event happens, all the listeners attached with instance.on(callback, context) will get triggered with the following event:

{
    x, // total distance scrolled on the x axis
    y, // total distance scrolled on the y axis
    deltaX, // distance scrolled since the last event on the x axis
    deltaY, // distance scrolled since the last event on the y axis
    originalEvent // the native event triggered by the pointer device or keyboard
}

Example

import VirtualScroll from 'virtual-scroll'

const scroller = new VirtualScroll()
scroller.on(event => {
    wrapper.style.transform = `translateY(${event.y}px)`
})

License

MIT.