app/javascript/mastodon/components/intersection_observer_article.js

   1 import React from 'react';
   2 import PropTypes from 'prop-types';
   3 import scheduleIdleTask from '../features/ui/util/schedule_idle_task';
   4 import getRectFromEntry from '../features/ui/util/get_rect_from_entry';
   5 import { is } from 'immutable';
   6
   7 // Diff these props in the "rendered" state
   8 const updateOnPropsForRendered = ['id', 'index', 'listLength'];
   9 // Diff these props in the "unrendered" state
  10 const updateOnPropsForUnrendered = ['id', 'index', 'listLength', 'cachedHeight'];
  11
  12 export default class IntersectionObserverArticle extends React.Component {
  13
  14   static propTypes = {
  15     intersectionObserverWrapper: PropTypes.object.isRequired,
  16     id: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
  17     index: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
  18     listLength: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
  19     saveHeightKey: PropTypes.string,
  20     cachedHeight: PropTypes.number,
  21     onHeightChange: PropTypes.func,
  22     children: PropTypes.node,
  23   };
  24
  25   state = {
  26     isHidden: false, // set to true in requestIdleCallback to trigger un-render
  27   }
  28
  29   shouldComponentUpdate (nextProps, nextState) {
  30     const isUnrendered = !this.state.isIntersecting && (this.state.isHidden || this.props.cachedHeight);
  31     const willBeUnrendered = !nextState.isIntersecting && (nextState.isHidden || nextProps.cachedHeight);
  32     if (!!isUnrendered !== !!willBeUnrendered) {
  33       // If we're going from rendered to unrendered (or vice versa) then update
  34       return true;
  35     }
  36     // Otherwise, diff based on props
  37     const propsToDiff = isUnrendered ? updateOnPropsForUnrendered : updateOnPropsForRendered;
  38     return !propsToDiff.every(prop => is(nextProps[prop], this.props[prop]));
  39   }
  40
  41   componentDidMount () {
  42     const { intersectionObserverWrapper, id } = this.props;
  43
  44     intersectionObserverWrapper.observe(
  45       id,
  46       this.node,
  47       this.handleIntersection
  48     );
  49
  50     this.componentMounted = true;
  51   }
  52
  53   componentWillUnmount () {
  54     const { intersectionObserverWrapper, id } = this.props;
  55     intersectionObserverWrapper.unobserve(id, this.node);
  56
  57     this.componentMounted = false;
  58   }
  59
  60   handleIntersection = (entry) => {
  61     this.entry = entry;
  62
  63     scheduleIdleTask(this.calculateHeight);
  64     this.setState(this.updateStateAfterIntersection);
  65   }
  66
  67   updateStateAfterIntersection = (prevState) => {
  68     if (prevState.isIntersecting !== false && !this.entry.isIntersecting) {
  69       scheduleIdleTask(this.hideIfNotIntersecting);
  70     }
  71     return {
  72       isIntersecting: this.entry.isIntersecting,
  73       isHidden: false,
  74     };
  75   }
  76
  77   calculateHeight = () => {
  78     const { onHeightChange, saveHeightKey, id } = this.props;
  79     // save the height of the fully-rendered element (this is expensive
  80     // on Chrome, where we need to fall back to getBoundingClientRect)
  81     this.height = getRectFromEntry(this.entry).height;
  82
  83     if (onHeightChange && saveHeightKey) {
  84       onHeightChange(saveHeightKey, id, this.height);
  85     }
  86   }
  87
  88   hideIfNotIntersecting = () => {
  89     if (!this.componentMounted) {
  90       return;
  91     }
  92
  93     // When the browser gets a chance, test if we're still not intersecting,
  94     // and if so, set our isHidden to true to trigger an unrender. The point of
  95     // this is to save DOM nodes and avoid using up too much memory.
  96     // See: https://github.com/tootsuite/mastodon/issues/2900
  97     this.setState((prevState) => ({ isHidden: !prevState.isIntersecting }));
  98   }
  99
 100   handleRef = (node) => {
 101     this.node = node;
 102   }
 103
 104   render () {
 105     const { children, id, index, listLength, cachedHeight } = this.props;
 106     const { isIntersecting, isHidden } = this.state;
 107
 108     if (!isIntersecting && (isHidden || cachedHeight)) {
 109       return (
 110         <article
 111           ref={this.handleRef}
 112           aria-posinset={index + 1}
 113           aria-setsize={listLength}
 114           style={{ height: `${this.height || cachedHeight}px`, opacity: 0, overflow: 'hidden' }}
 115           data-id={id}
 116           tabIndex='0'
 117         >
 118           {children && React.cloneElement(children, { hidden: true })}
 119         </article>
 120       );
 121     }
 122
 123     return (
 124       <article ref={this.handleRef} aria-posinset={index + 1} aria-setsize={listLength} data-id={id} tabIndex='0'>
 125         {children && React.cloneElement(children, { hidden: false })}
 126       </article>
 127     );
 128   }
 129
 130 }