hometown/app/javascript/mastodon/components/intersection_observer_article.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

137 lines
4.5 KiB
JavaScript

import React from 'react';
import PropTypes from 'prop-types';
import scheduleIdleTask from '../features/ui/util/schedule_idle_task';
import getRectFromEntry from '../features/ui/util/get_rect_from_entry';
import { is } from 'immutable';
// Diff these props in the "rendered" state
const updateOnPropsForRendered = ['id', 'index', 'listLength'];
// Diff these props in the "unrendered" state
const updateOnPropsForUnrendered = ['id', 'index', 'listLength', 'cachedHeight'];
export default class IntersectionObserverArticle extends React.Component {
static propTypes = {
intersectionObserverWrapper: PropTypes.object.isRequired,
id: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
index: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
listLength: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
saveHeightKey: PropTypes.string,
cachedHeight: PropTypes.number,
onHeightChange: PropTypes.func,
children: PropTypes.node,
currentlyViewing: PropTypes.number,
updateCurrentlyViewing: PropTypes.func,
};
state = {
isHidden: false, // set to true in requestIdleCallback to trigger un-render
}
shouldComponentUpdate (nextProps, nextState) {
const isUnrendered = !this.state.isIntersecting && (this.state.isHidden || this.props.cachedHeight);
const willBeUnrendered = !nextState.isIntersecting && (nextState.isHidden || nextProps.cachedHeight);
if (!!isUnrendered !== !!willBeUnrendered) {
// If we're going from rendered to unrendered (or vice versa) then update
return true;
}
// Otherwise, diff based on props
const propsToDiff = isUnrendered ? updateOnPropsForUnrendered : updateOnPropsForRendered;
return !propsToDiff.every(prop => is(nextProps[prop], this.props[prop]));
}
componentDidMount () {
const { intersectionObserverWrapper, id } = this.props;
intersectionObserverWrapper.observe(
id,
this.node,
this.handleIntersection
);
this.componentMounted = true;
if(id === this.props.currentlyViewing) this.node.scrollIntoView();
}
componentWillUnmount () {
const { intersectionObserverWrapper, id } = this.props;
intersectionObserverWrapper.unobserve(id, this.node);
this.componentMounted = false;
}
handleIntersection = (entry) => {
this.entry = entry;
if(entry.intersectionRatio > 0.75 && this.props.updateCurrentlyViewing) this.props.updateCurrentlyViewing(this.id);
scheduleIdleTask(this.calculateHeight);
this.setState(this.updateStateAfterIntersection);
}
updateStateAfterIntersection = (prevState) => {
if (prevState.isIntersecting !== false && !this.entry.isIntersecting) {
scheduleIdleTask(this.hideIfNotIntersecting);
}
return {
isIntersecting: this.entry.isIntersecting,
isHidden: false,
};
}
calculateHeight = () => {
const { onHeightChange, saveHeightKey, id } = this.props;
// save the height of the fully-rendered element (this is expensive
// on Chrome, where we need to fall back to getBoundingClientRect)
this.height = getRectFromEntry(this.entry).height;
if (onHeightChange && saveHeightKey) {
onHeightChange(saveHeightKey, id, this.height);
}
}
hideIfNotIntersecting = () => {
if (!this.componentMounted) {
return;
}
// When the browser gets a chance, test if we're still not intersecting,
// and if so, set our isHidden to true to trigger an unrender. The point of
// this is to save DOM nodes and avoid using up too much memory.
// See: https://github.com/tootsuite/mastodon/issues/2900
this.setState((prevState) => ({ isHidden: !prevState.isIntersecting }));
}
handleRef = (node) => {
this.node = node;
}
render () {
const { children, id, index, listLength, cachedHeight } = this.props;
const { isIntersecting, isHidden } = this.state;
if (!isIntersecting && (isHidden || cachedHeight)) {
return (
<article
ref={this.handleRef}
aria-posinset={index + 1}
aria-setsize={listLength}
style={{ height: `${this.height || cachedHeight}px`, opacity: 0, overflow: 'hidden' }}
data-id={id}
tabIndex='0'
>
{children && React.cloneElement(children, { hidden: true })}
</article>
);
}
return (
<article ref={this.handleRef} aria-posinset={index + 1} aria-setsize={listLength} data-id={id} tabIndex='0'>
{children && React.cloneElement(children, { hidden: false })}
</article>
);
}
}