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'; // 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, }; 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; } // If we are and remain hidden, diff based on props if (isUnrendered) { return !updateOnPropsForUnrendered.every(prop => nextProps[prop] === this.props[prop]); } // Else, assume the children have changed return true; } componentDidMount () { const { intersectionObserverWrapper, id } = this.props; intersectionObserverWrapper.observe( id, this.node, this.handleIntersection, ); this.componentMounted = true; } componentWillUnmount () { const { intersectionObserverWrapper, id } = this.props; intersectionObserverWrapper.unobserve(id, this.node); this.componentMounted = false; } handleIntersection = (entry) => { this.entry = entry; 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/mastodon/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; const style = {}; if (!isIntersecting && (isHidden || cachedHeight)) { style.height = `${this.height || cachedHeight || 150}px`; style.opacity = 0; style.overflow = 'hidden'; } return ( <article ref={this.handleRef} aria-posinset={index + 1} aria-setsize={listLength} data-id={id} tabIndex={0} style={style} > {children && React.cloneElement(children, { hidden: !isIntersecting && (isHidden || !!cachedHeight) })} </article> ); } }