Do not show "Adding new attribute failed" error message when loading of product screens is interrupted by page unload

[mattsherman]

Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

Why did this happen

In WooCommerce 7.8 the empty state handling for the attributes tab on the product editor updated (#38126) and then refactored to add an alert when the background request to get the empty attribute form failed (#38354).

Unfortunately, in Firefox (and possibly other browsers), these background requests fail (and the error handling associated with them are executed) when they are canceled due to the entire page being unloaded (Chrome appears to handle this differently, not executing the error handling for these canceled/failed background requests).

To make matters worse, the request to get the empty attribute form was being made when on the product edit/list screen ("All Products": /wp-admin/edit.php?post_type=product), when it really only is useful on the product screen ("Add New": /wp-admin/post-new.php?post_type=product and "Edit": /wp-admin/post.php?post=0000&action=edit).

The page can get unloaded while these background requests are in-progress in normal circumstances when the connection between the browser and the server is slow.

How to reproduce the issue in #38755

A few scenarios where this can be seen:

• Load "All Products" and quickly click a product to edit it, or sort the list by clicking one of the column headers
• Load a product to edit it and quickly navigate to a different page

These can be difficult to reproduce if the timing isn't right. I found that setting my network throttling to "Wi-Fi" in the Network tab of the browser developer tools made it more likely that this occurred.

Also, as mentioned, I have only seen this happen in Firefox.

What is changed in this PR

This PR fixes this error by:

• Only attempting to load the empty attribute form when editing a product (do not attempt to load it when viewing "All Products")
• Suppressing the "Adding new attribute failed" alert if the page is being unloaded

This PR does not stop the meta-boxes-product.js and meta-boxes-product-variation.js files from being enqueued for the edit-product screen ("All Products"). While I believe it to be unnecessary in that scenario, those files have been loaded for 5-10 years in that scenario and I want to dig into things a bit further to verify that changing that will introduce no issues that aren't immediately apparent. I will create a follow-up issue to handle this.

Also, note that in Firefox there still may be circumstances where messages such as the following still appear in the console:

Uncaught (in promise) Object { code: "fetch_error", message: "You are probably offline." }

These messages appeared prior to WooCommerce 7.8. Ideally they would suppressed, but that would be a more involved fix and should be handled separately in the future if desired.

Closes #38755.

How to test the changes in this Pull Request:

With Firefox:

1. Load "All Products" and quickly click a product to edit it, or sort the list by clicking one of the column headers
2. Do this a number of times and verify that you never see the "Adding new attribute failed" alert
3. Load a product to edit it and quickly navigate to a different page
4. Do this a number of times and verify that you never see the "Adding new attribute failed" alert
5. Repeat everything in Chrome to verify no issues exist there either
6. Verify that the empty state for the attributes tab is correct as detailed in Update empty state for product attributes tab #38126.

Empty state for attributes tab:

[github-actions]

Test Results Summary

Commit SHA: 03ddbbe

Test 🧪	Passed ✅	Failed 🚨	Broken 🚧	Skipped ⏭️	Unknown ❔	Total 📊	Duration ⏱️
API Tests	259	0	0	2	0	261	0m 50s
E2E Tests	189	0	0	19	0	208	21m 41s

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To view the full API test report, click here.
To view the full E2E test report, click here.
To view all test reports, visit the WooCommerce Test Reports Dashboard.

[github-actions]

Hi , @woocommerce/mothra

Apart from reviewing the code changes, please make sure to review the testing instructions as well.

You can follow this guide to find out what good testing instructions should look like:
https://github.com/woocommerce/woocommerce/wiki/Writing-high-quality-testing-instructions

[nathanss]

I was not able to reproduce the issue in Firefox with throttling, as described.

But based on your explanation and by reviewing the code, I think the fix makes a lot of sense, so I'm going to approve it.

[oujisan2236]

thank you its been driving me nuts everytiime i click on anything under products on wp-admin

[ptepartz]

Still getting this error in 7.9.0 - using google chrome (fully updated).