anchor.diff:  
   [source,clojure]
   ----
  -(ns hello-world.core
  -  (:require [clojure.browser.repl :as repl]))
  -
  -(defonce conn
  -  (repl/connect "http://localhost:9000/repl"))
  +(ns hello-world.core)
   
   (enable-console-print!)
   
  
positive.code: specify `:output-dir` so that the REPL can reuse compiled files
  generated by the build.
  
  We also need to modify our source to load the browser REPL:
  
  [source,clojure]
  ----
  (ns hello-world.core
    (:require [clojure.browser.repl :as repl]))
  
  (defonce conn
    (repl/connect "http://localhost:9000/repl"))
  
  (enable-console-print!)
  
  (println "Hello world!")
  ----
  
  We create the connection with `defonce`. This ensures the connection is
  constructed only one time - we may reload this namespace during
  development and we don't want multiple connection instances.
  
  Let's try it:
  
  [source,clojure]
  
negative.code: (cljs.build.api/build "src"
    {:main 'hello-world.core
     :output-to "out/main.js"
     :browser-repl true
     :verbose true})
  
  (cljs.repl/repl (cljs.repl.browser/repl-env)
  