To start, make sure to download the latest available version of CheerpJ [here](https://leaningtech.com/download-cheerpj/). Decompress the Cheerpj 2.3 archive anywhere, for example in ```~/cheerpj_2.3```.
**Important:** Converting an applet is documented at the bottom of this page.
# Converting a single JAR to a JAR.JS file
```cheerpjfy.py``` is an helper script that automatically takes care of unpacking, compiling and optimising a whole JAR archive. Using ```cheerpjfy.py``` is the recommended way of compiling applications and libraries using CheerpJ.
This command will generate a file called ```my_application_archive.jar.js```, which needs to be deployed in the same folder of the original .JAR archive, and hosted on a web server. Instructions on how to serve the converted JavaScript on a web page are provided below.
**Important:** The files _must_ be accessed through a Web server. Trying to open the HTML page directly from the disk is not supported. The URL must look like ```http://127.0.0.1:8080/cheerpj_test.html```, if it looks like ```file://c/users/Test/cheerpj_test.html``` CheerpJ won't be able to start.
**Note to Windows users:** You will need to have python3 installed on the system. Python provides a launcher called ```py``` that will automatically detect and use the right version of python for a given script. To use ```cheerpjfy.py``` on Windows you need to prefix all the commands with ```py```, for example:
This command will generate ```my_application_archive.jar.js``` but **not** ```my_dependency_archive.jar.js```. Each archive should be compiled separately by invoking ```~/cheerpj_2.3/cheerpjfy.py my_dependency_archive.jar```.
It is in general safe to put the target JAR in the ```--deps``` list, although it is not required. If you have an application composed of many JARs you can do something like this:
This page will initialize the CheerpJ system, create a graphical environment to contain all Java windows and then execute the ```main``` method of ```ChangeThisToYourClassName```. The second parameter of cheerpjRunMain is a ```:``` separated list of JARs where application classes can be found (the classpath). The ```/app/``` is a virtual file system mount point that reference the root of the web server this page is loaded from.
You can now serve this web page on a simple http server, such as the http-server utility.
Applets can be run by Chrome users using the [CheerpJ Applet Runner](https://chrome.google.com/webstore/detail/cheerpj-applet-runner-bet/bbmolahhldcbngedljfadjlognfaaein) Chrome extension. You can also compile the applet ahead of time using the method described above.
To support all browsers, you can add the following tags to your page:
This should be sufficient to get the applet to run on any browser, with the pre-compiled JAR.JS's files deployed in the same directory of the the original JAR files. The ```cheerpjInit({enablePreciseAppletArchives:true});``` call can be done during page initialization.
To avoid potential conflicts with native Java we recommend replacing the original HTML tag with ```cheerpj-``` prefixed version. You should use ```<cheerpj-applet>```, ```<cheerpj-object>``` or ```<cheerpj-embed>``` depending on the original tag.
