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WaitUntilOnPage: Fix scroll listener always registered + bump debounce ms

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## Issue
The scroll listener never unregisters, and is always registering itself on every scroll. I believe it was done that way to also handle the case of "element is already in viewport when mounted".

## Change
Tried to separate both "element is already in viewport when mounted" and "element scrolled into viewport" into different effects.

The timeout value used is a bit arbitrary, but is needed because the initial size is (0, 0), and to debounce any layout shifts. Reasoning: If an element is explicitly placed under this wrapper, the additional delay is acceptable since it's meant to be lazy-loaded anyway.
This commit is contained in:
infinite-persistence 2021-07-05 11:27:22 +08:00
parent 89576572f5
commit 9745d6df3e
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GPG key ID: B9C3252EDC3D0AA0
1 changed files with 37 additions and 22 deletions
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59
ui/component/common/wait-until-on-page.jsx
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@ -2,7 +2,7 @@
import React from 'react';
import debounce from 'util/debounce';
const DEBOUNCE_SCROLL_HANDLER_MS = 25;
const DEBOUNCE_SCROLL_HANDLER_MS = 50;
type Props = {
children: any,
@ -14,33 +14,48 @@ export default function WaitUntilOnPage(props: Props) {
const ref = React.useRef();
const [shouldRender, setShouldRender] = React.useState(false);
React.useEffect(() => {
const handleDisplayingRef = debounce((e) => {
const element = ref && ref.current;
if (element) {
const bounding = element.getBoundingClientRect();
if (
bounding.bottom >= 0 &&
bounding.right >= 0 &&
// $FlowFixMe
bounding.top <= (window.innerHeight || document.documentElement.clientHeight) &&
// $FlowFixMe
bounding.left <= (window.innerWidth || document.documentElement.clientWidth)
) {
setShouldRender(true);
}
const shouldElementRender = React.useCallback((ref) => {
const element = ref && ref.current;
if (element) {
const bounding = element.getBoundingClientRect();
if (
bounding.width > 0 &&
bounding.height > 0 &&
bounding.bottom >= 0 &&
bounding.right >= 0 &&
// $FlowFixMe
bounding.top <= (window.innerHeight || document.documentElement.clientHeight) &&
// $FlowFixMe
bounding.left <= (window.innerWidth || document.documentElement.clientWidth)
) {
return true;
}
}
return false;
}, []);
if (element && !shouldRender) {
window.addEventListener('scroll', handleDisplayingRef);
return () => window.removeEventListener('scroll', handleDisplayingRef);
// Handles "element is already in viewport when mounted".
React.useEffect(() => {
setTimeout(() => {
if (!shouldRender && shouldElementRender(ref)) {
setShouldRender(true);
}
}, 500);
}, []); // eslint-disable-line react-hooks/exhaustive-deps
// Handles "element scrolled into viewport".
React.useEffect(() => {
const handleDisplayingRef = debounce(() => {
if (shouldElementRender(ref)) {
setShouldRender(true);
}
}, DEBOUNCE_SCROLL_HANDLER_MS);
if (ref) {
handleDisplayingRef();
if (ref && ref.current && !shouldRender) {
window.addEventListener('scroll', handleDisplayingRef);
return () => window.removeEventListener('scroll', handleDisplayingRef);
}
}, [ref, setShouldRender, shouldRender]);
}, [ref, setShouldRender, shouldRender, shouldElementRender]);
const render = props.skipWait || shouldRender;