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remove costly ancestor observation for element visibility #277

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remove costly ancestor observation for element visibility #277

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11 changes: 5 additions & 6 deletions src/ch5-base/ch5-base-class.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1079,17 +1079,16 @@ export abstract class Ch5BaseClass extends HTMLElement implements ICh5CommonAttr
/**
* Initialize common mutation observer used in each component for checking component visibility
*
* The ancestor registration was removed for the reason documented on
* Ch5Common.initCommonMutationObserver(). Kept in sync with that method deliberately - no call site
* in this class is currently active, but the two implementations should not diverge.
*
* @param element
*/
// eslint-disable-next-line @typescript-eslint/no-unused-vars
public initCommonMutationObserver(element: Ch5BaseClass) {
this._commonMutationObserver = new Ch5MutationObserver(this);
this._commonMutationObserver.isConnected = true;

let target = element as HTMLElement;
while (Ch5MutationObserver.checkElementValidity(target)) {
this._commonMutationObserver.observe(target);
target = target.parentNode as HTMLElement;
}
}

public disconnectCommonMutationObserver() {
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18 changes: 12 additions & 6 deletions src/ch5-common/ch5-common.ts
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Expand Up @@ -1821,17 +1821,23 @@ export class Ch5Common extends HTMLElement implements ICh5CommonAttributes {
/**
* Initialize common mutation observer used in each component for checking component visibility
*
* The observer used to be registered on every ancestor of the component up to <body>, watching the
* 'style' and 'inert' attributes. Every notification read offsetParent and getComputedStyle in order
* to maintain elementIsVisible - a flag nothing reads, since the only two consumers (in ch5-image)
* are commented out. Measured on a project with ~2400 components across 17 preloaded pages: ~12k
* observe() registrations at load, and per page flip ~3600 observer callbacks doing ~13k
* getComputedStyle + offsetParent reads, about 65% of total page-flip time.
*
* The observer object is still created so that disconnectCommonMutationObserver() and its
* isNil/isEmpty guards keep working; only the ancestor registration is gone. Ch5BaseClass, used by
* the newer components, already has its initCommonMutationObserver() call commented out.
*
* @param element
*/
// eslint-disable-next-line @typescript-eslint/no-unused-vars
public initCommonMutationObserver(element: Ch5Common) {
this._commonMutationObserver = new Ch5MutationObserver(this);
this._commonMutationObserver.isConnected = true;

let target = element as HTMLElement;
while (Ch5MutationObserver.checkElementValidity(target)) {
this._commonMutationObserver.observe(target);
target = target.parentNode as HTMLElement;
}
}

public updateElementVisibilityInViewport(visibility: boolean) {
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