[wp-trac] [WordPress Trac] #47500: Optimize customizer load time

[WordPress Trac]

#47500: Optimize customizer load time
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 Reporter:  Nick_theGeek  |      Owner:  (none)
     Type:  enhancement   |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Customize     |    Version:
 Severity:  normal        |   Keywords:
  Focuses:  javascript    |
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 Please see some discussion in slack for background and ideas
 https://wordpress.slack.com/archives/C0381N237/p1559852377000600

 TLDR; More plugins and themes are using the customizer. It's a very good
 experience when making changes to options that affect the display of the
 site. As more controls are added the initial page render is taking longer
 and longer.

 Searching for things like "WordPress customizer long load times" results
 in tickets like
 https://wordpress.org/support/topic/customizer-takes-12-seconds-to-load/

 In my own tests against a plugin I develop for I've found DOM Ready load
 times approaching 10 seconds.

 In default usage this is not apparent, but as themes and plugins use the
 customizer it becomes very slow.

 Ideally the initial page render should be more complete and then panels,
 sections, and controls can be added. This will make the page "feel"
 complete and more responsive.

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Ticket URL: <https://core.trac.wordpress.org/ticket/47500>
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