anchor.diff:  JavaScript. There's about 6 1/2 megabytes worth of JavaScript in there. This may
   seem unweildy but fortunately the ClojureScript compiler generates output
   optimized for the Google Closure Compiler. The Google Closure Compiler performs
  -many optimizations, but the most significant for browser-based clients are
  +many optimizations and the most significant for browser-based clients are
   minification and dead code elimination.
   
  -Let's remove the dev time REPL bits from `src/hello_world/core.cljs`:
  +Let's remove the REPL modifications we made earlier from `src/hello_world/core.cljs`:
   
   [source,clojure]
   ----
  
positive.code: [[clojurescript-compiler]]
  === ClojureScript Compiler
  
  Find a good place to create a directory named `hello_world`. Then from _inside_
  this `hello_world` directory we will create a simple directory structure. Please
  note that in this directory the underscore convention in the file and directory
  names are significant and that you should follow this convention.
  
  [source,bash]
  ----
  
negative.code: Let's make a mistake. Try evaluating `(ffirst [1])`. You should get a
  source mapped stack trace pointing at ClojureScript source locations not
  JavaScript ones. This makes debugging a lot nicer.
  
  You can easily explore the options provided by the ClojureScript compiler
  by using `-h` or `--help`:
  
  [source,bash]
  ----
  clj -m cljs.main -h
  ----
  
  On Windows:
  
  [source,bash]
  ----
  java -cp "cljs.jar;src" -m cljs.main -h
  ----
  
  One important thing to note is that so called main options like `--compile`,
  `--main`, `--repl` must always come last.
  
  [[production-builds]]
  == Production Builds
  