I wanted to use functions from goog namespace although--as I found out later, I didn't have to because goog is already exists in my namespace. So, I put (:require [goog]) in a ns declaration. Then, when I tried to reload that particular namespace by doing :require :reload in a cljs repl, I got:

Error: Namespace "x.x.x" already declared.

Doing :require :reload again in the cljs repl makes the repl throws

Error: Namespace "cljs.user" already declared.
(NO_SOURCE_FILE)
(out/goog/base.js:273:40)

I tested the steps below using clojurescript 1.7.145 and 1.7.170.

Here are the steps to reproduce which are taken from clojurescript quickstart-browser repl section:

1. Download the standalone clojurescript 1.7.170 jar https://github.com/clojure/clojurescript/releases/download/r1.7.170/cljs.jar

2. Create a directory hello_world and copy the JAR into that directory, then from inside the hello_world directory:

3. repl.clj content

4. index.html content

5. src/hello_world/core.cljs content

6. run clojurescript repl

7. Open http://localhost:9000 in browser (I use google chrome). Open javascript console.

8. enter expression below in the clojurescript repl

10. Look the browser javascript console. Nothing new shown.

11. Quit from the repl using :cljs/quit

12. Add [goog] in ns declaration in src/hello_world/core.cljs so that the content of the file becomes:

13. Run the clojurescript repl again

14. Now refresh the http://localhost:9000 in browser. Make sure the javascript console stays open.

13. enter expression below in the clojurescript repl

it just returns nil

15. See the javascript console, it shows

16. Executing this expression again (require '[hello-world.core :as hello] :reload) shows nothing new in the browser's javascript console while the clojurescript repl throws