Generalized the infinite scrollable list (#4697)

1 files changed, 122 insertions, 0 deletions

diff --git a/app/javascript/mastodon/components/intersection_observer_article.js b/app/javascript/mastodon/components/intersection_observer_article.js
new file mode 100644
index 000000000..347767818
--- /dev/null
+++ b/app/javascript/mastodon/components/intersection_observer_article.js
@@ -0,0 +1,122 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import ImmutablePureComponent from 'react-immutable-pure-component';
+import scheduleIdleTask from '../features/ui/util/schedule_idle_task';
+import getRectFromEntry from '../features/ui/util/get_rect_from_entry';
+
+export default class IntersectionObserverArticle extends ImmutablePureComponent {
+
+  static propTypes = {
+    intersectionObserverWrapper: PropTypes.object,
+    id: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
+    index: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
+    listLength: PropTypes.oneOfType([PropTypes.string, PropTypes.number]),
+    children: PropTypes.node,
+  };
+
+  state = {
+    isHidden: false, // set to true in requestIdleCallback to trigger un-render
+  }
+
+  shouldComponentUpdate (nextProps, nextState) {
+    if (!nextState.isIntersecting && nextState.isHidden) {
+      // It's only if we're not intersecting (i.e. offscreen) and isHidden is true
+      // that either "isIntersecting" or "isHidden" matter, and then they're
+      // the only things that matter (and updated ARIA attributes).
+      return this.state.isIntersecting || !this.state.isHidden || nextProps.listLength !== this.props.listLength;
+    } else if (nextState.isIntersecting && !this.state.isIntersecting) {
+      // If we're going from a non-intersecting state to an intersecting state,
+      // (i.e. offscreen to onscreen), then we definitely need to re-render
+      return true;
+    }
+    // Otherwise, diff based on "updateOnProps" and "updateOnStates"
+    return super.shouldComponentUpdate(nextProps, nextState);
+  }
+
+  componentDidMount () {
+    if (!this.props.intersectionObserverWrapper) {
+      // TODO: enable IntersectionObserver optimization for notification statuses.
+      // These are managed in notifications/index.js rather than status_list.js
+      return;
+    }
+    this.props.intersectionObserverWrapper.observe(
+      this.props.id,
+      this.node,
+      this.handleIntersection
+    );
+
+    this.componentMounted = true;
+  }
+
+  componentWillUnmount () {
+    if (this.props.intersectionObserverWrapper) {
+      this.props.intersectionObserverWrapper.unobserve(this.props.id, this.node);
+    }
+
+    this.componentMounted = false;
+  }
+
+  handleIntersection = (entry) => {
+    if (this.node && this.node.children.length !== 0) {
+      // save the height of the fully-rendered element
+      this.height = getRectFromEntry(entry).height;
+
+      if (this.props.onHeightChange) {
+        this.props.onHeightChange(this.props.status, this.height);
+      }
+    }
+
+    this.setState((prevState) => {
+      if (prevState.isIntersecting && !entry.isIntersecting) {
+        scheduleIdleTask(this.hideIfNotIntersecting);
+      }
+      return {
+        isIntersecting: entry.isIntersecting,
+        isHidden: false,
+      };
+    });
+  }
+
+  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 } = this.props;
+    const { isIntersecting, isHidden } = this.state;
+
+    if (!isIntersecting && isHidden) {
+      return (
+        <article
+          ref={this.handleRef}
+          aria-posinset={index}
+          aria-setsize={listLength}
+          style={{ height: `${this.height}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} aria-setsize={listLength} data-id={id} tabIndex='0'>
+        {children && React.cloneElement(children, { hidden: false })}
+      </article>
+    );
+  }
+
+}