J2CL · 
Seamless Java in JavaScript applications that tightly optimizes with
Closure Compiler
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.
Guides
- Getting Started
- 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.
Last, the workflow is not yet supported in Windows. You can contribute to
make this a reality. Coordinate and follow the progress of this effort
here.
For developers that want to use Windows as their platform we recommend
installing under WSL (Windows Subsystem for Linux).
Stay tuned!
J2CL vs. GWT?
In early 2015, Google GWT team made a difficult but necessary decision to work
on a new alternative product to enable Java for the Web.
It was mostly due to changing trends in the web ecosystem and our new internal
customers who were looking at Java on the Web not as an isolated ecosystem but
an integral part of their larger stack. It required a completely new vision
to create tools from the ground up, that are tightly integrated with the rest of
the ecosystem. A modern architecture, that is reliable, fast and provides a
quick iteration cycle.
There was no practical way to achieve those goals completely incrementally out
of GWT. We started from scratch using everything we learned from working on GWT
over the years. In the meantime, we kept GWT steering committee members in the
loop and gave contributors very early access so they could decide to build the
next version of GWT on J2CL.
The strategy has now evolved GWT3 to an SDK focused on libraries and enterprise
tooling which was one of the strongest points of GWT all along.
We think that such separation of concerns is crucial part of the success of the
both projects and will provide the best results for the open source community.
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.