React Virtual Dynamic List

Yes, yet another React Virtual List... Why?

• Provides dynamic item heights
• Only measures what it draws, estimates the rest and keeps everything smooth by adjusting scroll position when sizes are discovered later
• Does not need to measure intermediate items when large scrolling, massively improving performance
• Does not need an accurate estimated item height
• Allows items to change size at any time
• Allows natural browser layout of the components on screen within their standard container, no individual item positioning
• Works in environments that don't constantly fire scroll events (e.g. iOS)

This component uses a O(Ln2) algorithm to work out the position of items and caches all of this for maximum performance even when scrolling huge distances.

Supports list of up to 1,000,000 pixels in height (due to browser limitations on pixel heights). Provides events that enable any number of items.

Installation

npm i react-virtual-dynamic-list

Usage

    <Virtual items={someCollection} renderItem={item=>(<div>{item.id}</div>)}/>

or

    <Virtual items={100000} renderItem={item=>(<div>Item number {item + 1}</div>)}/>

Parameters

(Required) items - array | number of items

Provides the items that will be rendered, if an array is used, the contents are passed to the renderItem function as context, otherwise the index is passed

(Required) renderItem - function (item|index, index)

A function to render the item. The first parameter is the item or the item's index. The second is always the index.

scrollTop - the scroll position of the component in pixels (default to 0)

scrollToItem - scroll to show the specified index at the top of the display

Wrapper - the wrapper for items in the grid (defaults to <div/>)

If you need your items to render properly inside a wrapper component then you can provide it here.

Your component must apply the style prop passed to it and render children

Holder - the overall holder for the grid (defaults to <div/>)

If want to provider a component to render the whole of the virtual list you can provide it here.

Your component must apply the style prop passed to it, take a ref via forwardRef and apply it to the root and render children

useAnimation - should animation be used to help position items e.g. for iOS (defaults to true)

Animation is used in addition to scrolling. A very minor overhead.

overscan - the number of component heights to apply as overscan (defaults to 1)

Provides a number of pages of overscan

expectedHeight - the expected height, can be very rough (defaults to 64)

Heights are worked out from averages after the first render, so something rough is fine.

onInit - function({getPositionOf, getHeightOf, getItemFromPosition, itemCache})

Provides access to some api functions that can be useful for modifying the list. Often you will cache these for later use.

onSize - function ({averageHeight, height, item})

Provides useful information on item sizes so you can resize the component, the most useful being averageHeight of an item based on the items drawn.

getPositionOf(item) - returns the position of an item

getHeightOf(item) - returns the height of an item (may be estimated if not measured)

getItemFromPosition(position) - gets the item that is at a scroll position

itemCache - a Map containing the cache of all currently rendered items, you can clear this

if you like at any time.

onScroll - function({items, start, last, scrollPos, max, scroller})

Provides an event that can modify the scroll. You may change items in this function. If you insert things above you are probably going to have to update the scroll position afterwards.

scroller - the element being scrolled

you might want to fiddle with scrollTop when you add things (especially if going upwards)

items - the items being rendererd

start - the first item being rendered (off screen above)

last - the last item being rendererd (off screen below)

max - the last item that has been rendered ever (useful for loading more)

Also contains the parameters passed to onInit

    function onScroll({max, items}) {
        if (max > items.length - 15) {
            items.push(...Array.from({length: 15}, (_, index) => ({
                id: index + items.length,
                height: Math.random() * 98 + 32 | 0,
                color: rgb(Math.random() * 112 + 143,
                    Math.random() * 112 + 143, Math.random() * 112 + 143)
            })))
        }
    }

OTHER PROPERTIES

Are passed to the wrapping div that does the scrolling (this is not Wrapper, that holds the actual items).

    <Virtual items={1000} renderItem={i=>(<div>{i}</div>)} width={80} height={200}/>

Sets the size of the rendered div to 80 x 200

ScrollIndicatorHolder

This is a component you can use as a Holder for the Virtual component. It uses shadows to indicate that scrolling is possible.

You can pass a shadow parameter throw to it via the Virtual.

    <Virtual shadow={'0 0 32px 14px black'} items={[...items]} Holder={ScrollIndicatorHolder} renderItem={item => {
        return <Item item={item}/>
    }}/>

useMeasurement

Provides the ability to measure a component using a resizeObserver - so it will redraw on resize too which is handy. ResizeObserver is pony filled.

    const [size, ref] = useMeasurement() 
    return <div ref={ref}>Something is {size.width} x {size.height} at {size.left}, {size.top} </div>