virtual-scroll

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.

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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 -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

#### 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.