# google/j2cl

Java to Closure JavaScript transpiler

Repository: https://github.com/google/j2cl
Canonical: https://ross.abutalabs.com/products/j2cl
Language: Java
License: Apache-2.0
License Family: permissive
Topics: j2cl, java, javascript, transpiler, compiler, gwt, wasm, wasmgc
Last push: 2026-08-26T18:34:18+00:00

## Health v2 (maintenance only)
Score: 83/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 53, longevity 100
- inputs: {"age_days": 3361, "days_push": 7, "days_rel": 153, "gap_med": 140.5, "n_releases_24m": 3}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1376, forks 160 (observed 2026-08-28T04:04:33.210908+00:00)

## What it is
J2CL is a transpiler from Google that converts Java source code into Closure-style JavaScript, tightly integrated with Closure Compiler for optimization. It also supports compiling Java to WebAssembly and is the technology behind Google's GSuite apps like Gmail and Docs.

## Use cases
- reuse existing Java libraries in a JavaScript web application
- compile Java code to JavaScript for the browser
- build web apps with Java on the frontend
- transpile Java to WebAssembly
- share business logic between Java backend and web frontend
- migrate a GWT application to modern tooling

## When to choose
- you have substantial Java code or Java libraries (Guava, Dagger) you want to run in the browser
- you want strong static typing and cross-language type checks in frontend code
- you already use Bazel and Closure Compiler tooling
- you want to target WebAssembly from Java

## When to avoid
- you are starting a greenfield frontend project with no Java investment
- you need full Java runtime semantics or reflection-heavy libraries
- you want a simple build without Bazel
- you need stable, finalized Wasm support

## Facets
- artifact type: library
- maturity: active
- function: compiler, build-tool, developer-tools
- domain: compilers, web-development, programming-languages, developer-tools
- platform: jvm, cross-platform
- tags: transpiler, java-to-javascript, closure-compiler, gwt, wasm, bazel, jsinterop, web-server

## Member repositories
- google/j2cl (main) score 83

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:04:33.210908+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T04:40:30.101821+00:00, confidence not recorded.
  - readme: https://github.com/google/j2cl (fetched 2026-08-28T04:04:33.210908+00:00, sha 71fb18638d36)
- Data as of 2026-08-30T08:39:29.467469+00:00.