Pre-load REST API index data to avoid FOMD

[danielbachhuber]

Because theme_supports data present in the index is used in rendering
UI, it'd be better to include it in the initial payload, instead of
incurring a second API request.

FOMD = Flash of Missing Data

Previously #6318 (comment)

[pento]

It seems like this causes the schema to be loaded twice: can the current schema usage be reworked to use the data preloaded from / as the source?

[danielbachhuber]

It seems like this causes the schema to be loaded twice: can the current schema usage be reworked to use the data preloaded from / as the source?

I'm not sure I follow. Can you clarify?

[aduth]

I noticed this in #6301, but I thought it was reasonable for this to be loaded asynchronously, particularly because we're doing a union with the current post's format (known/visible/selected at load-time)†.

I don't have a strong opposition to preloading it, though it speaks to a broader question of whether there's a line to be drawn for what should and shouldn't be preloaded. Or preload all the things?

† Only discussing current post formats usage. Other future usage could be more disruptive without preloading.

[danielbachhuber]

though it speaks to a broader question of whether there's a line to be drawn for what should and shouldn't be preloaded. Or preload all the things?

I'd think it would be of benefit to preload all data that will be present in the view. The data is going to be fetched anyway, and this would reduce the real-world overhead (which is loading WordPress again and again to serve API requests).

[pento]

In gutenberg_extend_wp_api_backbone_client(), we cache the result of / in wpApiSettings.schema already.

To reproduce, load Gutenberg, View Source, and search for theme_supports.

[danielbachhuber]

In gutenberg_extend_wp_api_backbone_client(), we cache the result of / in wpApiSettings.schema already.

Ah, but then we'd need to get this data into the store. Or, we could reference the global variable. The former seems much more desirable to the latter.

Any opinions on how to reconcile this difference?

[pento]

The schema data is only used here, that I'm aware of, so it should just be a case of loading it from the _wpAPIDataPreload global, instead. If you want to avoid referencing the global directly, then the cache export may be an option, or send a fake request to getCachedResponse().

[danielbachhuber]

@pento Given the uncertainty around a better approach, can we land this and then open an issue to improve upon it in the future?

[pento]

Yeah, let's go with this for now.

@danielbachhuber: Could you please open a new issue to track the problem of / being loaded twice?

[danielbachhuber]

Could you please open a new issue to track the problem of / being loaded twice?

Yep #6539