anchor.diff:  java -cp "cljs.jar;src" -m cljs.main -c hello-world.core -r
   ----
   
  -`-m`, which is short for `--main` invokes a Clojure function, in this case
  -`cljs.main`. The `cljs.main` function supports a variety of command line
  -arguments to specify common tasks. We're using `-c` for `--compile` to specify
  -that we want to compile the `hello-world.core` namespace. This is followed by
  -`-r` for `--repl` to say that we want a REPL to start immediately when compilation
  -completes.
  -
   Your default web browser will open to a page that looks like the following:
   
   After a couple of seconds you will see `Hello world!` print at the terminal and
  -you will be given a REPL prompt. Change your `src/hello_world/core.cljs` source
  -file to look like the following:
  +you will be given a REPL prompt. Try evaluating some expressions like
  +the following:
  +
  +[source,clojure]
  +----
  +(inc 1)
  +(map inc [1 2 3])
  +(.getElementById js/document "app")
  +----
  +
  +Let's look a bit closer at the flags we've used here. `-m`, short
  +for `--main`, invokes a _Clojure_ function, in this case `cljs.main`. The
  +`cljs.main` function supports a variety of command line arguments to specify
  +common tasks. We're using `-c` for `--compile` to specify that we want to
  +compile the `hello-world.core` namespace. This is followed by `-r` for `--repl`
  +to say that we want a REPL to launch immediately when compilation completes.
  +
  +Change your `src/hello_world/core.cljs` source file to look like the following:
   
   [source,clojure]
   ----
  
positive.code: (println "Hello world!")
  ----
  
  First we declare our namespace. This namespace must correspond to the location
  of the source file. We then print the famous message. Now that we have a simple
  program, let's build and run some ClojureScript:
  
  [source,bash]
  ----
  
negative.code: java -cp "cljs.jar;src" -m cljs.main -s
  ----
  
  `-s` is for `--serve`. This command does not start a REPL, so a browser window
  will not be automatically opened. Navigate to http://localhost:9000 using your
  favorite browser. Check the JavaScript Console, you should see `Hello world!`
  printed. The builtin web server gzips JavaScript content. Check your browser's
  JavaScript Console Network tab and you should be able to confirm that the total
  JavaScript payload is now around 20K.
  
  [[running-clojurescript-on-node.js]]
  == Running ClojureScript on Node.js
  
  First make sure you have Node.js installed. For instructions on installing Node.js, see the
  https://github.com/nodejs/node/blob/master/README.md[Node.js wiki]. Only
  the current stable versions of Node.js (>= `0.12.X`) are supported at
  this time.
  
  Before we proceed, enable source mapping:
  
  [source,bash]
  ----
  