Java to JavaScript Translator

A modular code translator (transpiler) from a simple Java-like language (“Mini-Java”) to JavaScript, implemented in JavaScript.

This project demonstrates how to implement a basic language transpiler: from tokenization and parsing, to AST generation and code output.

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Features

• Translates Mini-Java code (variable declarations, assignments, functions, arithmetic) to JavaScript
• Modular, readable code following SOLID principles
• Clear separation between lexer, parser, AST, code generator, and IO
• Easy to extend and experiment for learning, demos, or further development

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Project Structure

java-to-js-transpiler/
├── src/
│   ├── lexer.js
│   ├── token.js
│   ├── parser.js
│   ├── abstract-syntax-tree.js
│   ├── javascript-generator.js
│   ├── file-reader.js
│   └── main.js
├── examples/
│   └── sample.mjava
├── README.md
├── package.json

• src/lexer.js: Lexical analyzer—converts Mini-Java source code into tokens.
• src/token.js: Token class definition.
• src/parser.js: Parses the token stream into an Abstract Syntax Tree (AST).
• src/abstract-syntax-tree.js: AST node class definitions.
• src/javascript-generator.js: Converts the AST into equivalent JavaScript code.
• src/file-reader.js: Utility class for reading files.
• src/main.js: Entry point: glues all components together.
• examples/sample.mjava: Example input file written in Mini-Java.

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Getting Started

Prerequisites

• Node.js (version 16+ recommended)

Installation

Clone the repository or download the source code:

git clone https://github.com/robinsonur/java-to-js-transpiler.git
cd java-to-js-transpiler

Running the Translator

You can run the translator using the included start script:

npm start

Or directly with Node (default input is examples/sample.mjava):

node src/main.js

To translate another file:

node src/index.js path/to/your-file.mjava

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Example

Input (examples/sample.mjava):

int suma(int a, int b) {
  int resultado = a + b;
  return resultado;
}

int x = 5;
int y = 2;
int z = suma(x, y);

Output:

function suma(a, b) {
  let resultado = a + b;
  return resultado;
}

let x = 5;

let y = 2;

let z = suma(x, y);

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How It Works

1. Lexical Analysis: The lexer (src/lexer.js) reads the Mini-Java code and converts it into a sequence of tokens.

2. Parsing: The parser (src/parser.js) processes the token stream and constructs an Abstract Syntax Tree (AST), using class definitions from src/abstract-syntax-tree.js.

3. Code Generation: The JavaScript generator (src/javascript-generator.js) traverses the AST and produces JavaScript code.

4. Execution: The entry point (src/main.js) manages file input, executes the translation pipeline, and displays both the original Mini-Java code and its JavaScript output.

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Customization & Extension

• Modify or add AST nodes and update the code generator to support new features.
• Easily add support for more advanced statements, new types, or output formats.

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Author

Robinson U. Rodríguez GitHub