From 28cbfb9f10a7e9f136bcf287404958d83d3c4a6a Mon Sep 17 00:00:00 2001 From: Nolan Lawson Date: Sun, 28 May 2017 07:26:35 -0700 Subject: [PATCH] Simplify isIntersecting in status_list.js (#3371) --- .../mastodon/components/status_list.js | 27 +++++++++++++++---- 1 file changed, 22 insertions(+), 5 deletions(-) diff --git a/app/javascript/mastodon/components/status_list.js b/app/javascript/mastodon/components/status_list.js index b82c63a8428..59089ad9258 100644 --- a/app/javascript/mastodon/components/status_list.js +++ b/app/javascript/mastodon/components/status_list.js @@ -27,7 +27,8 @@ class StatusList extends ImmutablePureComponent { }; state = { - isIntersecting: [{ }], + isIntersecting: {}, + intersectionCount: 0, } statusRefQueue = [] @@ -65,15 +66,31 @@ class StatusList extends ImmutablePureComponent { attachIntersectionObserver () { const onIntersection = (entries) => { this.setState(state => { - const isIntersecting = { }; entries.forEach(entry => { const statusId = entry.target.getAttribute('data-id'); - state.isIntersecting[0][statusId] = entry.isIntersecting; + state.isIntersecting[statusId] = entry.isIntersecting; }); - return { isIntersecting: [state.isIntersecting[0]] }; + // isIntersecting is a map of DOM data-id's to booleans (true for + // intersecting, false for non-intersecting). + // + // We always want to return true in shouldComponentUpdate() if + // this object changes, because onIntersection() is only called if + // something has changed. + // + // Now, we *could* use an immutable map or some other structure to + // diff the full map, but that would be pointless because the browser + // has already informed us that something has changed. So we can just + // use a regular object, which will be diffed by ImmutablePureComponent + // based on reference equality (i.e. it's always "unchanged") and + // then we just increment intersectionCount to force a change. + + return { + isIntersecting: state.isIntersecting, + intersectionCount: state.intersectionCount + 1, + }; }); }; @@ -122,7 +139,7 @@ class StatusList extends ImmutablePureComponent { render () { const { statusIds, onScrollToBottom, scrollKey, shouldUpdateScroll, isLoading, isUnread, hasMore, prepend, emptyMessage } = this.props; - const isIntersecting = this.state.isIntersecting[0]; + const { isIntersecting } = this.state; let loadMore = null; let scrollableArea = null;