ClojureScript

To begin using ClojureScript, follow these resources:

• Quick Start Guide: https://clojurescript.org/guides/quick-start
• Official Documentation: https://clojurescript.org
• Tutorials: https://clojurescript.org/guides

If you have questions, feedback, or need to report issues, use the following channels:

• Mailing Lists: Clojure mailing list or the ClojureScript user mailing list.
• Chat: IRC channel #clojurescript on freenode.net or the Clojurians Slack channel.
• Bug/Feature Tracking: Jira.

Note: Before submitting issues, please review the Reporting Issues page.

When using :optimizations :advanced, external JavaScript calls may be optimized away, causing errors. To prevent this, you must compile your source with a referred externs file using the :externs option.

cljsc src '{:optimizations :advanced :output-to "hello-extern.js" :externs ["externs.js"]}'

Before using the ClojureScript CLI, perform the following setup steps:

1. Create a CLOJURESCRIPT_HOME environment variable pointing to your ClojureScript root directory.
2. Run the bootstrap script located at $CLOJURESCRIPT_HOME/script/bootstrap.
3. Add $CLOJURESCRIPT_HOME/bin to your system PATH.

Depending on your build tool, use the following dependency configurations to include ClojureScript (version 1.12.145) in your project.

### Clojure deps.edn
```clojure
org.clojure/clojurescript {:mvn/version "1.12.145"}

Leiningen

[org.clojure/clojurescript "1.12.145"]

Maven

<dependency>
  <groupId>org.clojure</groupId>
  <artifactId>clojurescript</artifactId>
  <version>1.12.145</version>
</dependency>

To use Closure Compiler's "advanced" optimization setting via cljsc, pass a Clojure map of compiler options.

Advanced mode produces a single .js file (twitterbuzz.js), requiring only one <script> tag in your HTML. To view the application compiled with these optimizations, open index-advanced.html.

cljsc src '{:optimizations :advanced}' > twitterbuzz.js

For faster development cycles, you can compile using a Clojure REPL.

1. Start the REPL using script/repl.
2. Once the REPL is active, evaluate the following code to build the project. Note that :output-dir is set to samples/twitterbuzz/out because the index.html script tag expects files in that directory.

For more compilation examples, consult the cljs.closure source code.

(use 'cljs.closure)
(def opts {:output-to "samples/twitterbuzz/twitterbuzz.js" :output-dir "samples/twitterbuzz/out"})

(build "samples/twitterbuzz/src" opts)

To compile your ClojureScript source files for development, use the cljsc command. This mode loads each file in a separate script tag, making it easier to track errors to specific files.

After compiling, open hello-dev.html in your browser to view the result.

cljsc src > hello.js

To prepare a project for a browser-connected REPL, you must first build the ClojureScript source files into JavaScript. This requires an HTML file and a ClojureScript file to establish the connection.

1. Navigate to the project directory.
2. Launch a Clojure REPL using the provided script.
3. Use cljs.closure to build the source directory into a target output directory.

cd samples/repl
../../script/repl

;; Inside the Clojure REPL:
(require '[cljs.closure :as cljsc])
(def opts {:output-to "main.js" :output-dir "out"})
(cljsc/build "src" opts)

A browser-connected REPL allows you to evaluate code where side-effects occur directly in the browser (e.g., manipulating the DOM or showing alerts).

To start the REPL using the browser as the evaluator, follow these steps in your Clojure REPL:

1. Require cljs.repl.
2. Require cljs.repl.browser.
3. Create a new evaluation environment using browser/repl-env.
4. Start the REPL with that environment using repl/repl.

After starting, open http://localhost:9000/ in your browser (or serve your local index.html via a webserver) to connect.

(require '[cljs.repl :as repl])
(require '[cljs.repl.browser :as browser])
(def env (browser/repl-env))
(repl/repl env)