virtual-scroll-pointer

> This fork supports PointerEvent for mouse or other pointer devices. See Usage & API Section below

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.

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- 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.

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``
npm i virtual-scroll-pointer -S
`

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#### 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_
- usePointer: if true, uses pointer events to simulate scrolling if is not a touch screen device, e.g. desktop with a mouse, _Defaults to true_
- pointerClickDelta: when usePointer is true, the minimum scroll delta pervent a click event being fired after pointerup, _Defaults 1 * window.devicePixelRatio,_

#### 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:

`js
{
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
}
`

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`js
import VirtualScroll from "virtual-scroll";

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

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MIT.