[wp-trac] [WordPress Trac] #28580: Speed up customizer by lazy-loading panels/sections/controls and settings as needed

[WordPress Trac]

#28580: Speed up customizer by lazy-loading panels/sections/controls and settings
as needed
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 Reporter:  westonruter  |       Owner:
     Type:  enhancement  |      Status:  assigned
 Priority:  normal       |   Milestone:  Future Release
Component:  Customize    |     Version:  3.4
 Severity:  normal       |  Resolution:
 Keywords:  needs-patch  |     Focuses:  javascript, rest-api
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Comment (by celloexpressions):

 We need to be careful not to make the experience worse. Often when
 implementing single page apps or single page JS-driven sites that rely
 heavily on Ajax requests, the experience actually feels slower than a
 normal pageload because users don't get the traditional browser feedback
 that a new page is loading.

 I remain extremely skeptical of loading controls "as-needed" since users
 could easily navigate to a section and then end up waiting for something
 to load. If we go that route, we'll need to benchmark the load time for
 accessing individual elements versus loading everything up front and prove
 that the change is a usability improvement for a majority of cases.
 Individual Ajax calls can be very slow in many places regardless of how
 much data we're loading, to the extend that loading everything at once is
 often better for UX.

 Rather than lazy-loading everything, we could have much more impactful
 changes if the lazy-loading is used in more refined situations such as:
 - Loading everything via Ajax when the customizer is bootstrapped from the
 front end, rather than loading pieces more granularly
 - Menu item and widget controls and settings could be loaded when the
 associated panels are first expanded, so that they don't impact initial
 load but are ready by the time a user navigates (note that menu item
 controls aren't rendered to the DOM until the associated menu section is
 expanded, which is a great balance in terms of speed/performance and
 scales easily to hundreds of menu items).
 - Theme controls don't need to be loaded until the themes panel is
 expanded (which is how #37661 handles things).
 - It may be reasonable to wait to load panel controls until the panel is
 expanded, but you'd want the sections there already.

 Generally, my concern is that "just-in-time" loading will really end up
 being "just-too-late" and usability would suffer as a result. We also need
 to think about how this would impact things like visible edit shortcuts,
 partials, and autofocusing. Loading things on demand sounds shiny but
 isn't necessarily the best approach for users (Calypso suffers
 horrifically here on poor internet connections).

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Ticket URL: <https://core.trac.wordpress.org/ticket/28580#comment:31>
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