lein_appendix_d.html

<section data-type="appendix" id="appendix_server_cljs">
<h1>ClojureScript on the Server</h1>

  <section data-type="sect1">
  <h1>ClojureScript on the Server</h1>

  <p>Just as JavaScript works in the browser and on the server, via a library like <a href="https://nodejs.org">Node.js</a>, so does ClojureScript. In this book I’m using Node.js for the server side.</p>

    <section data-type="sect2" id="getting-node">
    <h2>Getting Node.js</h2>
    <p>
    You can get Node.js from <a href="https://nodejs.org/download/">the download page</a>. This will also give you <em>npm</em>, Node’s package manager.
    </p>
    </section>
    
    <section data-type="sect2" id="create-node-project">
    <h2>Creating a ClojureScript/Node Project</h2>
    <p>
    I am using the minimal <em>mies-node</em> template to create a ClojureScript project that works with Node.js. Use the <code>git</code> utility to download the latest version and install it:
    </p>
    
<pre data-type="programlisting">[etudes@localhost ~]$ <strong>git clone https://github.com/swannodette/mies-node-template.git</strong>
Cloning into 'mies-node-template'...
remote: Counting objects: 114, done.
remote: Total 114 (delta 0), reused 0 (delta 0), pack-reused 114
Receiving objects: 100% (114/114), 14.78 KiB | 0 bytes/s, done.
Resolving deltas: 100% (46/46), done.
Checking connectivity... done.
[etudes@localhost ~]$ <strong>cd mies-node-template</strong>
[etudes@localhost mies]$ <strong>lein install</strong>
Created /home/etudes/mies-node-template/target/lein-template-0.3.0.jar
Wrote /home/etudes/mies-node-template/pom.xml
Installed jar and pom into local repo.</pre>

    <p>
    Here is the file structure that came from the command <code>lein&#160;new&#160;mies-node&#160;example</code>:
    </p>
    
<pre>example
├── project.clj
├── script
│   ├── compile
│   ├── compile.clj
│   ├── repl
│   ├── repl.clj
│   ├── watch
│   └── watch.clj
└── src
    └── example
        └── core.cljs</pre>
        
    <p>
    The <em>project.clj</em> file contains information about your project’s requirements and dependencies. The <em>script</em> directory contains scripts that:
    </p>
  
    <ul>
      <li>Open a REPL (<em>repl</em>)</li>
      <li>Compile your project project (<em>compile</em>)</li>
      <li>Compile parts of the ClojureScript system so you don’t have to recompile them every time you rebuild the project (<em>compile_cljsc</em>)</li>
      <li>Monitor the source directory and rebuild the project whenever a source file changes (<em>watch</em>)</li>
    </ul>
    
    <p>
    The <em>core.cljs</em> file will contain your code. For a new project, it looks like this:
    </p>
    
<pre>(ns example.core
  (:require [cljs.nodejs :as nodejs]))

(nodejs/enable-util-print!)

(defn -main []
  (println "Hello world!"))

(set! *main-cli-fn* -main)</pre>

    <p>
    You can, from the main <em>example</em> folder, invoke <em>script/compile</em>to build the project and start the browser REPL with <em>script/repl</em>. All these scripts use Leiningen, which will automatically retrieve any dependencies that your project needs. You will eventually see something like this:
    </p>
    
<pre>[etudes@localhost example]$ <strong>script/repl</strong>
ClojureScript Node.js REPL server listening on 57065
To quit, type: :cljs/quit
cljs.user=> </pre>
    
    <p>
    To run the program:
    </p>
    
    <pre>[etudes@localhost example]$ <strong>node example.js</strong>
Hello world!</pre>
    
    </section>

    <section data-type="sect2" id="integrating-node">
    <h2>Using Node.js Modules</h2>
    <p>
    To use a Node.js module, you need to define a binding for the library via the <code>js/require</code> function. You can then use that binding’s methods and properties in your ClojureScript code. The following is a REPL session that shows the use of the built-in <code>os</code> module.
    </p>
    
<pre>example.core=&gt; (def os (js/require "os"))
;; much output omitted
example.core=&gt; (.hostname os)
"localhost.localdomain"
example.core=&gt; (.platform os)
"linux"
example.core=&gt; (.-EOL os) ;; this is a property
"\n"</pre>
    </section>
  </section>
</section>