This article from 2016 is the only one about facets I can find: https://developers.suitecommerce.com/get-started-with-facets it says there's a facet object in SC.Shopping.Configuration.js but it's not there in 2019.2. Is there an updated reference? Where do I modify the facet fields from the default to a slider or color swatches?

Setup > SuiteCommerce Advanced > Configuration (Select the domain), there is Facet configuration sub tab where you can manage your facets there.

I'm aware of that area, thank you... I"m talking about how to change the display template for the facet type. For example, to change colors into swatches. The guide says there's a facet object in SC.Shopping.Configuration.js but it's not there in 2019.2. I need to know where in the SCA code to find this section now.

I'm a bit confused by your message. William is correct to point you to the configuration record. Everything that was in the configuration files has been moved to the configuration record. You can change what template to use for each facet in the configuration record page.