perf(focus-monitor): optimize event registration #18667
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Improve focus-monitor scalability by implementing event delegation instead of adding individual 'focus' and 'blur' event listeners to each monitored element.
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* perf(focus-monitor): optimize event registration Improve focus-monitor scalability by implementing event delegation instead of adding individual 'focus' and 'blur' event listeners to each monitored element. * Fix a bug in _getFocusOrigin(). * Add a comment explaining why we need to walk up the tree * Cleanup
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In angular#18667 event delegation was implemented for the `FocusMonitor` which is based around binding a single event on the `document`. The problem is that the browser won't invoke the `focus` and `blur` handlers on the `document`, if focus is moved within the same shadow root. These changes switch to delegating the events either through the closest shadow root or the `document`. Fixes angular#19133.
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In #18667 event delegation was implemented for the `FocusMonitor` which is based around binding a single event on the `document`. The problem is that the browser won't invoke the `focus` and `blur` handlers on the `document`, if focus is moved within the same shadow root. These changes switch to delegating the events either through the closest shadow root or the `document`. Fixes #19133.
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In #18667 event delegation was implemented for the `FocusMonitor` which is based around binding a single event on the `document`. The problem is that the browser won't invoke the `focus` and `blur` handlers on the `document`, if focus is moved within the same shadow root. These changes switch to delegating the events either through the closest shadow root or the `document`. Fixes #19133.
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In angular#18667 event delegation was implemented for the `FocusMonitor` which is based around binding a single event on the `document`. The problem is that the browser won't invoke the `focus` and `blur` handlers on the `document`, if focus is moved within the same shadow root. These changes switch to delegating the events either through the closest shadow root or the `document`. Fixes angular#19133.
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Improve
FocusMonitorscalability by implementing event delegation instead of adding individualfocusandblurevent listeners to each monitored element.The global listeners do have to walk up the ancestor chain of event target in order to support
checkChildren, but this is extremely fast even for very deeply nested DOM trees since all it has to do is callMap.has(element)for each one.Another potential improvement may be to store the tracked elements in a
WeakMapand remove the need to callstopMonitoring(), making the API easier, but this would require always keeping the 6 global event listeners active. Right now, they are removed if there are no tracked elements.