Given
(ns foo.core)
(defn square [x]
(* x x))
then do this in a REPL
cljs.user=> (require '[foo.core :refer [square]])
nil
cljs.user=> (var square)
#'foo.core/square
cljs.user=> (square 3)
9
cljs.user=> (ns-interns 'cljs.user)
{}
cljs.user=> (defn square [x] (+ x x))
WARNING: square already refers to: foo.core/square being replaced by: cljs.user/square at line 1 <cljs repl>
#'foo.core/square
cljs.user=> (square 3)
6
cljs.user=> (var square)
#'foo.core/square
cljs.user=> (in-ns 'foo.core)
nil
foo.core=> (square 3)
6
foo.core=> (in-ns 'cljs.user)
nil
cljs.user=> (ns-interns 'cljs.user)
{square #'cljs.user/square}
cljs.user=> (cljs.user/square 3)
TypeError: Cannot read property 'call' of undefined
at repl:1:105
at repl:9:3
at repl:14:4
at Object.exports.runInThisContext (vm.js:54:17)
at Domain.<anonymous> ([stdin]:41:34)
at Domain.run (domain.js:221:14)
at Socket.<anonymous> ([stdin]:40:25)
at emitOne (events.js:77:13)
at Socket.emit (events.js:169:7)
at readableAddChunk (_stream_readable.js:146:16)
cljs.user=> #'cljs.user/square
#'cljs.user/square
cljs.user=> @#'cljs.user/square
nil