hometown/app/javascript/mastodon/components/scrollable_list.js
Matt Panaro 31f7c3fc5d Summary: fix slowness due to layout thrashing when reloading a large … (#12661)
* Summary: fix slowness due to layout thrashing when reloading a large set of status updates

in order to limit the maximum size of a status in a list view (e.g. the home timeline), so as to avoid having to scroll all the way through an abnormally large status update (see https://github.com/tootsuite/mastodon/pull/8205), the following steps are taken:
•the element containing the status is rendered in the browser
•its height is calculated, to determine if it exceeds the maximum height threshold.
Unfortunately for performance, these steps are carried out in the componentDidMount(/Update) method, which also performs style modifications on the element.  The combination of  height request and style modification during javascript evaluation in the browser leads to layout-thrashing, where the elements are repeatedly re-laid-out (see https://developers.google.com/web/fundamentals/performance/rendering/avoid-large-complex-layouts-and-layout-thrashing & https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Performance_best_practices_for_Firefox_fe_engineers).
The solution implemented here is to memoize the collapsed state in Redux the first time the status is seen (e.g. when fetched as part of a small batch, to populate the home timeline) , so that on subsequent re-renders, the value can be queried, rather than recalculated.  This strategy is derived from https://github.com/tootsuite/mastodon/pull/4439 & https://github.com/tootsuite/mastodon/pull/4909, and should resolve https://github.com/tootsuite/mastodon/issues/12455.

Andrew Lin (https://github.com/onethreeseven) is thanked for his assistance in root cause analysis and solution brainstorming

* remove getSnapshotBeforeUpdate from status

* remove componentWillUnmount from status

* persist last-intersected status update and restore when ScrollableList is restored

e.g. when navigating from home-timeline to a status conversational  thread and <Back again

* cache currently-viewing status id to avoid calling redux with identical value

* refactor collapse toggle to pass explicit boolean
2019-12-29 05:39:48 +01:00

354 lines
11 KiB
JavaScript

import React, { PureComponent } from 'react';
import { ScrollContainer } from 'react-router-scroll-4';
import PropTypes from 'prop-types';
import IntersectionObserverArticleContainer from '../containers/intersection_observer_article_container';
import LoadMore from './load_more';
import LoadPending from './load_pending';
import IntersectionObserverWrapper from '../features/ui/util/intersection_observer_wrapper';
import { throttle } from 'lodash';
import { List as ImmutableList } from 'immutable';
import classNames from 'classnames';
import { attachFullscreenListener, detachFullscreenListener, isFullscreen } from '../features/ui/util/fullscreen';
import LoadingIndicator from './loading_indicator';
const MOUSE_IDLE_DELAY = 300;
export default class ScrollableList extends PureComponent {
static contextTypes = {
router: PropTypes.object,
};
static propTypes = {
scrollKey: PropTypes.string.isRequired,
onLoadMore: PropTypes.func,
onLoadPending: PropTypes.func,
onScrollToTop: PropTypes.func,
onScroll: PropTypes.func,
trackScroll: PropTypes.bool,
shouldUpdateScroll: PropTypes.func,
isLoading: PropTypes.bool,
showLoading: PropTypes.bool,
hasMore: PropTypes.bool,
numPending: PropTypes.number,
prepend: PropTypes.node,
alwaysPrepend: PropTypes.bool,
emptyMessage: PropTypes.node,
children: PropTypes.node,
bindToDocument: PropTypes.bool,
currentlyViewing: PropTypes.number,
updateCurrentlyViewing: PropTypes.func,
};
static defaultProps = {
trackScroll: true,
};
state = {
fullscreen: null,
cachedMediaWidth: 250, // Default media/card width using default Mastodon theme
};
intersectionObserverWrapper = new IntersectionObserverWrapper();
handleScroll = throttle(() => {
if (this.node) {
const scrollTop = this.getScrollTop();
const scrollHeight = this.getScrollHeight();
const clientHeight = this.getClientHeight();
const offset = scrollHeight - scrollTop - clientHeight;
if (400 > offset && this.props.onLoadMore && this.props.hasMore && !this.props.isLoading) {
this.props.onLoadMore();
}
if (scrollTop < 100 && this.props.onScrollToTop) {
this.props.onScrollToTop();
} else if (this.props.onScroll) {
this.props.onScroll();
}
if (!this.lastScrollWasSynthetic) {
// If the last scroll wasn't caused by setScrollTop(), assume it was
// intentional and cancel any pending scroll reset on mouse idle
this.scrollToTopOnMouseIdle = false;
}
this.lastScrollWasSynthetic = false;
}
}, 150, {
trailing: true,
});
mouseIdleTimer = null;
mouseMovedRecently = false;
lastScrollWasSynthetic = false;
scrollToTopOnMouseIdle = false;
setScrollTop = newScrollTop => {
if (this.getScrollTop() !== newScrollTop) {
this.lastScrollWasSynthetic = true;
if (this.props.bindToDocument) {
document.scrollingElement.scrollTop = newScrollTop;
} else {
this.node.scrollTop = newScrollTop;
}
}
};
clearMouseIdleTimer = () => {
if (this.mouseIdleTimer === null) {
return;
}
clearTimeout(this.mouseIdleTimer);
this.mouseIdleTimer = null;
};
handleMouseMove = throttle(() => {
// As long as the mouse keeps moving, clear and restart the idle timer.
this.clearMouseIdleTimer();
this.mouseIdleTimer = setTimeout(this.handleMouseIdle, MOUSE_IDLE_DELAY);
if (!this.mouseMovedRecently && this.getScrollTop() === 0) {
// Only set if we just started moving and are scrolled to the top.
this.scrollToTopOnMouseIdle = true;
}
// Save setting this flag for last, so we can do the comparison above.
this.mouseMovedRecently = true;
}, MOUSE_IDLE_DELAY / 2);
handleWheel = throttle(() => {
this.scrollToTopOnMouseIdle = false;
}, 150, {
trailing: true,
});
handleMouseIdle = () => {
if (this.scrollToTopOnMouseIdle) {
this.setScrollTop(0);
}
this.mouseMovedRecently = false;
this.scrollToTopOnMouseIdle = false;
}
componentDidMount () {
this.attachScrollListener();
this.attachIntersectionObserver();
attachFullscreenListener(this.onFullScreenChange);
// Handle initial scroll posiiton
this.handleScroll();
}
getScrollPosition = () => {
if (this.node && (this.getScrollTop() > 0 || this.mouseMovedRecently)) {
return { height: this.getScrollHeight(), top: this.getScrollTop() };
} else {
return null;
}
}
getScrollTop = () => {
return this.props.bindToDocument ? document.scrollingElement.scrollTop : this.node.scrollTop;
}
getScrollHeight = () => {
return this.props.bindToDocument ? document.scrollingElement.scrollHeight : this.node.scrollHeight;
}
getClientHeight = () => {
return this.props.bindToDocument ? document.scrollingElement.clientHeight : this.node.clientHeight;
}
updateScrollBottom = (snapshot) => {
const newScrollTop = this.getScrollHeight() - snapshot;
this.setScrollTop(newScrollTop);
}
getSnapshotBeforeUpdate (prevProps) {
const someItemInserted = React.Children.count(prevProps.children) > 0 &&
React.Children.count(prevProps.children) < React.Children.count(this.props.children) &&
this.getFirstChildKey(prevProps) !== this.getFirstChildKey(this.props);
const pendingChanged = (prevProps.numPending > 0) !== (this.props.numPending > 0);
if (pendingChanged || someItemInserted && (this.getScrollTop() > 0 || this.mouseMovedRecently)) {
return this.getScrollHeight() - this.getScrollTop();
} else {
return null;
}
}
componentDidUpdate (prevProps, prevState, snapshot) {
// Reset the scroll position when a new child comes in in order not to
// jerk the scrollbar around if you're already scrolled down the page.
if (snapshot !== null) {
this.setScrollTop(this.getScrollHeight() - snapshot);
}
}
cacheMediaWidth = (width) => {
if (width && this.state.cachedMediaWidth !== width) {
this.setState({ cachedMediaWidth: width });
}
}
componentWillUnmount () {
this.clearMouseIdleTimer();
this.detachScrollListener();
this.detachIntersectionObserver();
detachFullscreenListener(this.onFullScreenChange);
}
onFullScreenChange = () => {
this.setState({ fullscreen: isFullscreen() });
}
attachIntersectionObserver () {
this.intersectionObserverWrapper.connect({
root: this.node,
rootMargin: '300% 0px',
});
}
detachIntersectionObserver () {
this.intersectionObserverWrapper.disconnect();
}
attachScrollListener () {
if (this.props.bindToDocument) {
document.addEventListener('scroll', this.handleScroll);
document.addEventListener('wheel', this.handleWheel);
} else {
this.node.addEventListener('scroll', this.handleScroll);
this.node.addEventListener('wheel', this.handleWheel);
}
}
detachScrollListener () {
if (this.props.bindToDocument) {
document.removeEventListener('scroll', this.handleScroll);
document.removeEventListener('wheel', this.handleWheel);
} else {
this.node.removeEventListener('scroll', this.handleScroll);
this.node.removeEventListener('wheel', this.handleWheel);
}
}
getFirstChildKey (props) {
const { children } = props;
let firstChild = children;
if (children instanceof ImmutableList) {
firstChild = children.get(0);
} else if (Array.isArray(children)) {
firstChild = children[0];
}
return firstChild && firstChild.key;
}
setRef = (c) => {
this.node = c;
}
handleLoadMore = e => {
e.preventDefault();
this.props.onLoadMore();
}
handleLoadPending = e => {
e.preventDefault();
this.props.onLoadPending();
// Prevent the weird scroll-jumping behavior, as we explicitly don't want to
// scroll to top, and we know the scroll height is going to change
this.scrollToTopOnMouseIdle = false;
this.lastScrollWasSynthetic = false;
this.clearMouseIdleTimer();
this.mouseIdleTimer = setTimeout(this.handleMouseIdle, MOUSE_IDLE_DELAY);
this.mouseMovedRecently = true;
}
render () {
const { children, scrollKey, trackScroll, shouldUpdateScroll, showLoading, isLoading, hasMore, numPending, prepend, alwaysPrepend, emptyMessage, onLoadMore } = this.props;
const { fullscreen } = this.state;
const childrenCount = React.Children.count(children);
const loadMore = (hasMore && onLoadMore) ? <LoadMore visible={!isLoading} onClick={this.handleLoadMore} /> : null;
const loadPending = (numPending > 0) ? <LoadPending count={numPending} onClick={this.handleLoadPending} /> : null;
let scrollableArea = null;
if (showLoading) {
scrollableArea = (
<div className='scrollable scrollable--flex' ref={this.setRef}>
<div role='feed' className='item-list'>
{prepend}
</div>
<div className='scrollable__append'>
<LoadingIndicator />
</div>
</div>
);
} else if (isLoading || childrenCount > 0 || hasMore || !emptyMessage) {
scrollableArea = (
<div className={classNames('scrollable', { fullscreen })} ref={this.setRef} onMouseMove={this.handleMouseMove}>
<div role='feed' className='item-list'>
{prepend}
{loadPending}
{React.Children.map(this.props.children, (child, index) => (
<IntersectionObserverArticleContainer
key={child.key}
id={child.key}
index={index}
listLength={childrenCount}
intersectionObserverWrapper={this.intersectionObserverWrapper}
saveHeightKey={trackScroll ? `${this.context.router.route.location.key}:${scrollKey}` : null}
currentlyViewing={this.props.currentlyViewing}
updateCurrentlyViewing={this.props.updateCurrentlyViewing}
>
{React.cloneElement(child, {
getScrollPosition: this.getScrollPosition,
updateScrollBottom: this.updateScrollBottom,
cachedMediaWidth: this.state.cachedMediaWidth,
cacheMediaWidth: this.cacheMediaWidth,
})}
</IntersectionObserverArticleContainer>
))}
{loadMore}
</div>
</div>
);
} else {
scrollableArea = (
<div className={classNames('scrollable scrollable--flex', { fullscreen })} ref={this.setRef}>
{alwaysPrepend && prepend}
<div className='empty-column-indicator'>
{emptyMessage}
</div>
</div>
);
}
if (trackScroll) {
return (
<ScrollContainer scrollKey={scrollKey} shouldUpdateScroll={shouldUpdateScroll}>
{scrollableArea}
</ScrollContainer>
);
} else {
return scrollableArea;
}
}
}