CODEWITHSUNDEEP
google-chrome-extension
user3423014
user3423014

Reputation:

Event pages and background pages

Since there's no clear explanation in Chrome Extensions documentation, I came here for help.

I learned that background pages are basically invented to extend the extension's lifetime, and designed to hold values or keep the "engine" running in background so no one notices it. Because once you click on the extension's icon, you get what they call it, a "popup", and once you click outside the "popup" it disappears immediately and most important the extension "dies" (its lifetime ends).

So far we are good and everything is nice but: event pages are invented after that
and they are basically background pages that only work when they are called (to provide more memory space).

If that's the case, then wouldn't that be contradictory? What's the use of event pages if they only work when they're called?

Upvotes: 8

Views: 4582

Answers (1)

Xan
Xan

Reputation: 77523

Sometimes background pages only need to respond to events outside them (messages, web requests, button clicks, etc.)

In that case, an event page makes sense. It's not completely unloaded as if the extension is stopped - it defines its event handlers (what it wants to listen to) and then it's shut down until needed. Consider this to be "I'm going to sleep; don't wake me up unless A happens."

The difference with your example: closed popup ceases to exist completely, while Chrome remembers it needs to call a particular extension on particular events. If that event happens, the background page is started again an the event is fired in it.

This saves resources, but not always appropriate. Shutting down background page's context wipes its local state; it must be saved in various storage APIs instead of variables. If the local state is complex, it may not be worth the effort. Also, if your extension needs to react really fast or really often, suspend/resume may prove to be a performance hit.

All in all, event pages are not a complete replacement for background pages; that's why they are optional and not default. There are many things to consider when making an event page.

P.S. Regarding your "popup as most important part of the extension": this is exactly why it can't be the most important part in most cases. Usually, a background page is also used alongside a popup to keep event listeners and local state.

Upvotes: 8

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