README.md

J2CL

Seamless Java in JavaScript applications that tightly optimizes with Closure

J2CL is a powerful, simple and lightweight transpiler from Java to Closure style JavaScript.

• Get the best out of Java and JavaScript. You no longer need to choose between the two or lock into a specific framework or a language. Choose the right language at the right place and hire the best talent for the job.

• Get it correct the first time. The robust run-time type checking based on the strong Java type system combined with the advanced cross language type checks catches your mistakes early on.

• Provides massive code reuse. J2CL closely follows the Java language semantics. This reduces surprises, enables reuse across different platforms and brings most popular Java libraries into your toolkit including Guava, Dagger and AutoValue.

• Modern, fresh and blazing fast. Powered by Bazel, J2CL provides a fast and modern development experience that will make you smile and keep you productive.

• Road tested and trusted. J2CL is the underlying technology of the most advanced GSuite apps developed by Google including GMail, Inbox, Docs, Slides and Calendar.

Getting Started

Clone the repository and build a sample app from source:

• Install Bazel.

• Clone this repository:

      $ git clone https://github.com/google/j2cl.git

• Build a sample app:

      $ cd j2cl/samples/helloworld
      $ bazel build src/main/java/com/google/j2cl/samples/helloworld:helloworld

• Look at the optimized output:

      $ cat bazel-bin/src/main/java/com/google/j2cl/samples/helloworld/helloworld.js
      document.write('Hello from Java! and JS!');

Live-reload

ibazel is file-system watcher that auto-triggers bazel build when neeeded. To use it, just replace bazel with ibazel in any command:

• Install ibazel and make sure it is in your path.

• Run the development server

      $ cd j2cl/samples/helloworld
      $ ibazel run src/main/java/com/google/j2cl/samples/helloworld:helloworld_dev_server

• Navigate to 'http://localhost:6006/helloworld_dev.html" in your browser.

• Edit any source (e.g. HelloWorld.java), save and see the results. You will enjoy it more as it warms up!

You like build-on-save but you would like to refresh on your own terms? Pass -nolive_reload while running ibazel.

Setting up your first project

To start your first project, you can use the helloworld sample as a template:

      $ cp -R <j2cl-repo>/samples/helloworld <my-repo>/<app-name>

and you are done.

Guides

• JsInterop Cookbook
• J2CL Best Practices
• Emulation Limitations
• Bazel Tutorial
• Bazel Best Practices

Get Support

• Please subscribe to J2CL announce for announcements (low traffic).
• Please report bugs or file feature requests via issue tracker.
• For other questions you can also use the issue tracker for now.

Caveat Emptor

J2CL is production ready and actively used by many of Google's products, but the process of adapting workflows and tooling for the open-source version is not yet finalized and breaking changes will most likely be introduced. We are actively working on adapting more pieces including Junit4 emulation and faster pruning for an even better development experience. Stay tuned!

Contributing

Read how to contribute to J2CL.

Licensing

Please refer to the license file.

Disclaimers

J2CL is not an official Google product and is currently in 'alpha' release for developer preview.