[wp-trac] [WordPress Trac] #54884: Load scripts conditionally to reduce page loading and processing time

[WordPress Trac]

#54884: Load scripts conditionally to reduce page loading and processing time
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 Reporter:  galbaras       |       Owner:  (none)
     Type:  enhancement    |      Status:  new
 Priority:  normal         |   Milestone:  Awaiting Review
Component:  Script Loader  |     Version:
 Severity:  normal         |  Resolution:
 Keywords:                 |     Focuses:  javascript, performance
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Comment (by seebeen):

 Depends on the webpack setup.
 Polyfills are used to provide modern JS funcionality to older browsers.
 For example - https://caniuse.com/?search=es7 is the browser feature set -
 you can see which minimum version of the browser supports
 array.prototype.includes.

 Before doing any of the conditional loading, injecting polyfills, etc. I
 think it would best to agree on a minimum supported browser version. From
 there we can see which polyfills we would actually need.

 Additionally, conditionally loading jQuery migrate can be a potential
 hurdle, because the main reason it's there is because theme and plugin
 authors use deprecated jQuery APIs.

 To summarize:
 1) Polyfills are used for browser backward compatibility
 2) jQuery migrate is used for theme / plugin compatibility with newer
 versions of wordpress.

 To achieve your end goal you'd need to load a detector JS file early in
 the page loading process, and it cannot be an asynchronous load or a
 deffered one. Script would need to block JS execution, do the detection
 and shim in the polyfill / jQuery migrate. That can and will break caching
 plugin, but a side-effect would be a slower and more complex page load.

 To end on a high note - I think your proposal regarding wp-embed.js is
 awesome. WooCommerce already has conditionals to check if a website
 request is for the embed version
 {{{
 Constants::is_defined('IFRAME_REQUEST')
 }}}

 in order to prevent plugin updates when viewing embedded version of the
 site. The code and the detection can be backported to WP and only load the
 required embed JS / CSS when viewing the website from iframe.

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Ticket URL: <https://core.trac.wordpress.org/ticket/54884#comment:4>
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