sidePanel API: lifecycle events

[fregante]

Our extension uses sidebar to display extra content about the current website, the content script communicates to the sidebar, acting as a controller.

It would be useful to have more control over it, specifically, to only do operations when the sidebar is open or know when it's opened/closed.

Proposal: lifecycle events

Some example useful events could be:

• sidePanel.onLoad (the document/context is loaded)
  • somewhat possible via manual .sendMessage to all the relevant contexts
• sidePanel.onUnload (the document/context is unloaded/closed)
  • impossible via chrome.runtime.connect's onDisconnect event if there are multiple sidebars open, because the connection is preserved across instances: https://stackoverflow.com/a/36465331
  • impossible via onbeforeunload because .sendMessage doesn't complete

Some other more specific events could be:

• sidePanel.onShow (like visibilitychange, the current extension's sidePanel is shown)
• sidePanel.onHide (the user selects another extension's sidepanel)

These two are less important, I suppose a local visibilitychange + runtime.sendMessage could work as well.

[yankovichv]

+1 🙏.

Here are my similar requests - https://groups.google.com/a/chromium.org/g/chromium-extensions/c/cJmdMLmpbjg

[tophf]

Why can't you use the existing DOM visibilitychange event in the side panel to inform the connected content script?

Answered below in #517 (comment)

impossible via chrome.runtime.connect's onDisconnect event if there are multiple sidebars open, because the connection is preserved across instances: https://stackoverflow.com/a/36465331

No, each instance [of the content script] has one connection (port), which is what the linked answer says in different words.

[tophf]

sidePanel.onLoad (the document/context is loaded)
somewhat possible via manual .sendMessage to all the relevant contexts

It's unclear what benefits an event would provide that aren't achievable just as easily via sendMessage. An example of code might be helpful.

[yankovichv]

Why can't you use the existing DOM visibilitychange event in the side panel to inform the connected content script?

Any tricks of trying to track the visibility of our extension in the side panel via document.hidden or via clients.matchAll() didn't work. When the user switches between OS applications or minimizes the browser, we get a message that the document is invisible, which makes sense. So we need a native sidepanel API method to report show/hide and window Id accurately.

[tophf]

I see, so onShow/onHide or onVisibilityChanged event is necessary, but I don't see the need for the other two (onLoad/onUnload).

[yankovichv]

Yep, this, this is not so critical.

Although I would like to have such a common event for all contexts that may occur in chrome.runtime.getContext - https://developer.chrome.com/docs/extensions/reference/api/runtime#method-getContexts

For now, it’s easier to use a poll every 5 seconds.

[tophf]

I wouldn't call frequent polling an acceptable workaround. The point in my comments above was that this should be already possible via Port events.

[fregante]

Polling is not an alternative. By that suggestion, you don't need almost any events, you can just poll it.

Events are useful specifically because they let you avoid polling. That's the whole point of events: you want to respond to changes immediately without continuously waking up the background worker.

[tophf]

to respond to changes immediately without continuously waking up the background worker.

So this seems to answer my question above and hence should be added to the description of the proposal, because currently it only mentions the content script for which a runtime Port should already work. A port doesn't work well for the background script because in order to use a port's onDisconnected event we would have to keep the background script alive either by performing an action or by calling a special API every 30 seconds.