J2TS Runtime

92.0.0 verified Fri May 01 auth: no javascript

Runtime library required for code transpiled by the Java2TypeScript (J2TS) transpiler. Stable version 92.0.0 provides a set of Java-like utilities (e.g., ArrayList, HashMap) for TypeScript/JavaScript environments. Release cadence is tied to the J2TS transpiler. Key differentiator: enables running Java-derived code directly on Node.js or in browsers with minimal overhead. Only use as a dependency for J2TS projects.

Common errors

error Cannot find module 'j2ts-jre' ↓

cause Package not installed or missing from package.json.

fix

Run 'npm install j2ts-jre'

error TypeError: ArrayList is not a constructor ↓

cause Incorrect import pattern (e.g., default import instead of named import).

fix

Use 'import { ArrayList } from 'j2ts-jre''

error Module not found: Error: Can't resolve 'j2ts-jre/src/ArrayList' ↓

cause Deep importing internal modules instead of using the main export.

fix

Import from the package root: 'import { ArrayList } from 'j2ts-jre''

Warnings

gotcha Package is a runtime dependency for J2TS transpiled code. Do not manually add unless you are using the J2TS transpiler. ↓

fix Follow J2TS documentation for setup.

breaking Breaking changes occur frequently with major version bumps due to transpiler compatibility. See J2TS changelog. ↓

fix Upgrade both J2TS and j2ts-jre together.

deprecated Some Java methods may be deprecated in future versions. Check source for deprecation warnings. ↓

fix Use alternative methods as indicated in documentation.

Install

npm install j2ts-jre

yarn add j2ts-jre

pnpm add j2ts-jre

Imports

ArrayList

wrong

const ArrayList = require('j2ts-jre').ArrayList

correct

import { ArrayList } from 'j2ts-jre'

ESM-only package. No default export.

HashMap

wrong

import HashMap from 'j2ts-jre'

correct

import { HashMap } from 'j2ts-jre'

Named export. Default import will fail.

StringBuilder

wrong

import { StringBuilder } from 'j2ts-jre/src/index'

correct

import { StringBuilder } from 'j2ts-jre'

Do not deep-import internal paths.

RuntimeExportedClass
```
import { RuntimeExportedClass } from 'j2ts-jre'
```
Any class from J2TS is exported from the package root.

Quickstart

Demonstrates creating an ArrayList, adding elements, accessing by index, and iteration.

import { ArrayList } from 'j2ts-jre';

// Create an ArrayList and add elements
const list = new ArrayList<string>();
list.add('hello');
list.add('world');
console.log(list.size()); // 2

// Iterate
for (let i = 0; i < list.size(); i++) {
  console.log(list.get(i));
}