This is a hack that you probably shouldn't use in production, because I've only accounted for the home page. But it represents a change Magento core needs to make at some point: decomposing monolithic libraries down to their individual pieces.
Similar work should be done for Knockout bindings and utilities.
This repo comes with the non-bundled version of jQueryUI (same version as Magento 2.3). All core modules that rely on jquery/ui have had their dependency lists modified to import just the jQueryUI widgets they need.
If no direct import of jquery/ui is present on page load, only the used widgets will be loaded. If an extension or theme code has jquery/ui in it, this module will fall back to loading all widgets, to prevent the page from breaking.
In a real implementation, you would not copy all the core JS like I've done in view/frontend/web/hacks. Instead we'd be making the updates in Magento core.
Collected using 2.3-develop branch, with Luma and magento2-sample-data, on the homepage of the store.
Before
- Compressed (gzip): 125kb
- Uncompressed: 497kb
After
- Compressed (gzip): 63.2kb
- Uncompressed: 281kb