webExtension Storage API, StorageArea.set(), note about browser differences

[carlosjeurissen]

MDN URL

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage/StorageArea/set

What specific section or headline is this issue about?

Syntax > Parameters > keys

What information was incorrect, unhelpful, or incomplete?

As mentioned here:
w3c/webextensions#263

Setting a value to undefined has inconsistent behaviour across browsers.

What did you expect to see?

Have a warning noting the difference between the behaviour of setting a value to undefined.

In Firefox, setting a value to undefined will actually set it to undefined, while in other browsers, setting something to undefined is simply ignored and the original value is kept.

Do you have any supporting links, references, or citations?

As mentioned here:
w3c/webextensions#263

In there, @Rob--W mentioned the relevant bug reports:

• Bug 1499842 - "chrome.storage.sync.set({'existingKey': undefined}): inconsistency with Chromium"
  https://bugzilla.mozilla.org/show_bug.cgi?id=1499842
• Issue 896503: chrome.storage.sync.set({'existingKey': undefined}): inconsistency with Firefox
  https://bugs.chromium.org/p/chromium/issues/detail?id=896503

Do you have anything more you want to share?

No response

MDN metadata

Page report details

• Folder: en-us/mozilla/add-ons/webextensions/api/storage/storagearea/set
• MDN URL: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage/StorageArea/set
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/mozilla/add-ons/webextensions/api/storage/storagearea/set/index.md
• Last commit: 1d0e4c0
• Document last modified: 2022-04-21T05:20:11.000Z

[Rob--W]

Let's wait at least a week so that we can decide on the Firefox side how to address this inconsistency. If we decide to fix this, then the documentation update can be part of the bug resolution.

[Rob--W]

We triaged the bug at https://bugzilla.mozilla.org/show_bug.cgi?id=1499842 and decided that we'd like to change the behavior to match Chrome and Safari.

Regardless of the fix, the documentation should be updated as follows:

• The recommendation for removing values is to use storageArea.remove
• The recommendation for overwriting values with a void value is to use null (not undefined)
• The behavior of calling storageArea.set({keyname: undefined}) is inconsistent across browsers. Chrome and Safari do NOT change the value of keyname, while Firefox currently overwrites keyname with undefined (or sometimes null, e.g. in the storage.sync API). The recommendation is to NOT use undefined as a value, but use one of the other two options for consistent behavior.

[rebloor]

Fixed by #30101