Super Fantastic!

Initially, I wanted to download and cache id, title, slug, and except, but was disappointed that the REST API v2 did not support that. This plugin allowed me to define a concise response payload. In my case,

wp-json/wp/v2/posts?_query=[].{id: id, title: title.rendered, slug: slug, excerpt: excerpt.rendered}

Brilliant! Thank you elyobo!