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React Intersection List builds on top of React Intersection Observer, using a sentinel in the DOM to deliver a high-performance and smooth scrolling experience, even on low-end devices.
Table of Contents
- How to - FAQ - Props - Examples
And optionally the polyfill:
Next create a
Note that
The implementation follows these steps:
This element specifies
The
The prop
Do I always need to assign the
What's the
I am getting a console warning when I first load the list
Why doesn't the list render my updated list element(s)? The list renders items based on its props. An update somewhere else in your app (or within your list item) might update your list element(s), but if your list's
Are you planning to implement a "virtual list mode" like react-virtualized? Yes, there's already an open issue to implement a mode using occlusion culling. It will be implemented in a future release. If you can't wait, you could help us out by opening a Pull Request :)
gets call once for each item. | |
root element, often returning a scrollable element. | |
as spacing before the sentinel hits the edge of the list's viewport. | |
Before you do, please read our Code of Conduct so you know what we expect when you contribute to our projects.
Our Contributing Guide tells you about our development process and what we're looking for, gives you instructions on how to issue bugs and suggest features, and explains how you can build and test your changes.
Haven't contributed to an open source project before? No problem! Contributing Guide has you covered as well.
Agent Smith: ...we have no choice but to continue as planned. Deploy the sentinels. Immediately.
React Intersection List builds on top of React Intersection Observer, using a sentinel in the DOM to deliver a high-performance and smooth scrolling experience, even on low-end devices.
Table of Contents
- How to - FAQ - Props - Examples
Getting Started
$ npm install --save @researchgate/react-intersection-list
And optionally the polyfill:
$ npm install --save intersection-observer
Next create a
<List>
and two instance methods as props children
and
itemRenderer
:import React, { Component } from 'react';
import List from '@researchgate/react-intersection-list';
export default class InfiniteList extends Component {
itemsRenderer = (items, ref) => (
<ul className="list" ref={ref}>
{items}
</ul>
);
itemRenderer = (index, key) => <li key={key}>{index}</li>;
render() {
return (
<List
itemCount={1000}
itemsRenderer={this.itemsRenderer}
renderItem={this.itemRenderer}
/>
);
}
}
Note that
<List>
is a PureComponent
so it can keep itself from re-rendering.
It's highly recommended to avoid creating new functions for renderItem
and
itemsRenderer
so that it can successfully shallow compare props on re-render.Why React Intersection List?
The approach to infinite scrolling was commonly done by devs implementing throttledscroll
event callbacks. This keeps the main thread unnecessarily
busy... No more! IntersectionObservers
invoke callbacks in a low-priority
and asynchronous way by design.Agent Smith: Never send a human to do a machine's job.
The implementation follows these steps:
- Add a sentinel close to the last item in the list
- Update the list moving the internal cursor
- Trigger a callback when the sentinel comes into view
- Reposition the recycled sentinel at the end
- Repeat (∞) ?
Documentation
How to
Provided anitemsRenderer
prop you must attach the ref
argument to your
scrollable DOM element:<div ref={ref}>{items}</div>
This element specifies
overflow: auto|scroll
and it'll become the
IntersectionObserver root
. If the overflow
property isn't found, then
window
will be used as the root
instead.The
sentinel
element is by default detached from the list when the current
size reaches the available length, unless you're using awaitMore
. In case your
list is in memory and you rely on the list for incremental rendering only, the
default detaching behavior suffices. If you're loading more items in an
asynchoronous way, make sure you switch awaitMore
once you reach the total
length (bottom of the list).The prop
itemCount
must be used if the prop items
is not provided, and
viceversa. Calculating the list size is done by adding the current size and the
page size until the items' length is reached.FAQ
Why am I receiving too manyonIntersection
callbacks
We extend PureComponent
. That means, if the parent component re-renders and the props passed to your <List />
don't
hold the same reference anymore, the list re-renders and we accidentally restart the IntersectionObserver
of the Sentinel
.
Do I always need to assign the
ref
?
Yes, the ref callback will be used as the root
and is forwarded to the IntersectionObserver
within the Sentinel
.
What's the
threshold
value, and why does it need a unit?
The threshold
value is the amount of space needed before the sentinel
intersects with the root. The prop is
transformed into a valid rootMargin
property for the IntersectionObserver
, depending on the axis
you select. As a
sidenote, we believe that a percentage unit works best for responsive layouts.
I am getting a console warning when I first load the list
The sentinel detected a viewport with a bigger size than the size of its items...The prop
pageSize
is 10
by default, so make sure you're not falling short on items when you first render the
component. The idea of an infinite scrolling list is that items overflow the viewport, so that users have the impression that there're always more items available.
Why doesn't the list render my updated list element(s)? The list renders items based on its props. An update somewhere else in your app (or within your list item) might update your list element(s), but if your list's
currentLength
prop for instance, remains unchanged, the list prevents a
re-render. Updating the entire infinite list when one of its items has changed is far from optimal. Instead, update each item individually with some form of connect()
function or observables.
Are you planning to implement a "virtual list mode" like react-virtualized? Yes, there's already an open issue to implement a mode using occlusion culling. It will be implemented in a future release. If you can't wait, you could help us out by opening a Pull Request :)
Props
| property | type | default | description | | --------------------- | ------------------------------------------------------------------ | ---------------------------------------------- | ------------------------------------------------------------------------------------------------------- | |renderItem/children
| (index: number, key: number) => React.Element
| (index, key) => <div key={key}>{index}</div>
| render function as children or render props;gets call once for each item. | |
itemsRenderer
| (items: Array(React.Element), ref: HTMLElement) => React.Element
| (items, ref) => <div ref={ref}>{items}</div>
| render function for the list'sroot element, often returning a scrollable element. | |
itemCount/items
| number/Array (or Iterable Object)
| 0
| item count to render. |
| awaitMore
| boolean
| | if true keeps the sentinel from detaching. |
| onIntersection
| (size: number, pageSize: number) => void
| | invoked when the sentinel comes into view. |
| threshold
| string
| 100px
| value in absolute px
or %
as spacing before the sentinel hits the edge of the list's viewport. | |
axis
| string
| y
| scroll direction: y
== vertical and x
== horizontal |
| pageSize
| number
| 10
| number of items to render each hit. |
| initialIndex
| number
| 0
| start position of iterator of items. |Examples
Find multiple examples under: https://researchgate.github.io/react-intersection-list/Contributing
We'd love your help on creating React Intersection List!Before you do, please read our Code of Conduct so you know what we expect when you contribute to our projects.
Our Contributing Guide tells you about our development process and what we're looking for, gives you instructions on how to issue bugs and suggest features, and explains how you can build and test your changes.
Haven't contributed to an open source project before? No problem! Contributing Guide has you covered as well.