Much inspiration was taken from https://github.com/miikka/vega-tools-example for the current version of the app.
If you dont use emacs, then in a terminal do:
$ lein figwheel
(... cruft ...)
dev:cljs.user=> (in-ns 'vega-vis.core)
nil
dev:vega-vis.core!{:conn 2}=> (load "core")
nil
dev:vega-vis.core!{:conn 2}=> (swap! app-state assoc :data (:bar examples))
(... cruft ...)
dev:vega-vis.core!{:conn 2}=> (parse-input)
#<Promise[~]>
Start your cider repl normally with C-c M-j
(use 'figwheel-sidecar.repl-api)
(start-figwheel!)