onChanged callback object content clarification

[rebloor]

Description

Clarifies that the storage.onChanged callback triggered as a result of storageArea.set only returns changed details.

Related issues and pull requests

Fixes #31203

[github-actions]

Preview URLs

• /en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage/StorageArea/onChanged
• /en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage/onChanged

External URLs (2)

URL: /en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage/StorageArea/onChanged
Title: storage.StorageArea.onChanged

• https://bugzil.la/1833153 (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage/onChanged
Title: storage.onChanged

• https://bugzil.la/1833153 (1 time) (Note! This may be a new URL 👀)

(comment last updated: 2024-03-04 15:46:28)

[erosman]

The issue had to be updated.
Please hold the PR.

Sorry for the inaccurate test results.

[rebloor]

@erosman updated based on your issue revisions

[erosman]

Just a note which may save some developers some time.
Feel free to include something about it or not.

While Firefox storage onChanged (currently, see Bug 1833153) returns all the values and Chrome (currently) only the changed values, the target storage area still contains all the values e.g.

// same for browser and chrome APIs
browser.storage.onChanged.addListener()
browser.storage.sync.onChanged.addListener()

// the following contains all the values passed to the storage sync, changed and unchanged
browser.storage.sync.get()

[rebloor]

@erosman sorry, I'm unclear what the note about get would achieve if the developers were trying to observe changed keys.

[erosman]

@erosman sorry, I'm unclear what the note about get would achieve if the developers were trying to observe changed keys.

When developing a cross-browser-compatible extension, API inconsistency is a major concern. [1]
What I came up with in this case was to use onChanged as a trigger and then get all the values from storage.sync.get(), the same way Firefox returns onChanged.
While that is not necessary in all the cases, it is helpful in some cases (especially when a large values has to be segmented). [2]

I don't know if it is something worth mentioning or not, and feel free to disregard it.

Please also note

1. Inconsistency: storage onChanged
2. Proposal: Increase maximum item size in Storage sync quotas

[jpmedley]

So, Firefox can pass changes for multiple areas, but everyone else only does one at a time? Do I understand this correctly?

[rebloor]

@jpmedley, as I understand it, the difference is that Firefox returns all the keys from the storage area, whereas other browsers only return the changed ones only.

[jpmedley]

Sorry for the delay. I had a long weekend. I don't usually request multiple passes of changes. I'm making an exception because I think we need to clarify the difference between Firefox and other browsers.