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Cleaned up intersection observer when the component unmounts #1583

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merged 2 commits into from
Jan 4, 2021
Merged

Cleaned up intersection observer when the component unmounts #1583

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57752c8
Cleaning up the intersection observer and added additional comments
maufcost Oct 5, 2020
d070ada
* Tweaks comment
zachberry Oct 12, 2020
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2 changes: 1 addition & 1 deletion packages/app/obojobo-document-engine/__tests__/Viewer/components/viewer-app.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -727,7 +727,7 @@ describe('ViewerApp', () => {
expect(window.IntersectionObserver).toHaveBeenCalledWith(thisValue.onIntersectionChange, {
root: null,
rootMargin: '0px',
threshhold: 0
threshold: 0
})
expect(thisValue.observer.observe).toHaveBeenCalledWith(
FocusUtil.getVisuallyFocussedModel().getDomEl()
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11 changes: 10 additions & 1 deletion packages/app/obojobo-document-engine/src/scripts/viewer/components/viewer-app.js
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Expand Up @@ -170,6 +170,9 @@ export default class ViewerApp extends React.Component {
componentWillUnmount() {
this.unRegisterStores()
document.removeEventListener('visibilitychange', this.onVisibilityChange)

// Removing the intersection observer.
this.stopObservingForIntersectionChanges()
}

shouldComponentUpdate(nextProps, nextState) {
Expand Down Expand Up @@ -387,6 +390,10 @@ export default class ViewerApp extends React.Component {
this.stopObservingForIntersectionChanges()
const focusState = this.state.focusState

// Only creates an Intersection Observer object when the 'visualFocusTarget'
// property of 'focusState' is set - this is when all of the elements of the
// page are faded except for the visualFocusTarget (for example, when answering
// a practice question)
if (!focusState.visualFocusTarget) {
return
}
Expand All @@ -401,10 +408,12 @@ export default class ViewerApp extends React.Component {
return
}

// If an intersection observer is created below, we're 100% sure that
// 'focusState.visualFocusTarget' is set.
this.observer = new IntersectionObserver(this.onIntersectionChange, {
root: null,
rootMargin: '0px',
threshhold: 0
threshold: 0
})

this.observer.observe(el)
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