Interpreter

An interpreter that can recognize a JS-like language. It can parse very simple JavaScript programs but is still missing a bunch of features. I intend to finish it once I have some time off freelancing. The plan is to have the parser recognize all the syntactical elements of ECMA-262 and once there, generate Java bytecode (or LLVM IR) based on the AST which can be interpreted by a VM (JVM or LLVM).

Building and Running the Tests

Building and running the tests is a two-stage process.

Clone the repository

git clone https://github.com/devsh0/JsInterpreter.git

Run tests

cd JsInterpreter
mvn test

Note: Ubuntu doesn't play nice with maven 3.6.x. If you encounter an error, upgrade to maven 3.8.x.

Example Usecase

Although the interpreter isn't ready to be used as a standalone library, you can still take it for a test drive. Steps to do that are pretty straight-forward:

1. Install the library to your local maven repository.

cd JsInterpreter
mvn install

2. Create new Maven project and add the following dependency in pom.xml.

<dependency>
    <groupId>org.devsh0</groupId>
    <artifactId>JsInterpreter</artifactId>
    <version>0.1</version>
</dependency>

Also add this property to help the exec plugin find your main class. Replace com.my.package with your own package specifier.

<properties>
    <exec.mainClass>com.my.package.Main</exec.mainClass>
</properties>

3. Create a JavaScript source file in your project root and paste the following code.

function fizzbuzz(input) {
    let value = "";
    if (input % 3 == 0)
        value += "fizz";
    if (input % 5 == 0)
        value += "buzz";
    return value;
}
// By default, the last expression is fed back to Java as output.
fizzbuzz(10);

4. Create Main.java for your main class in src/main/java and paste the following code.

public class Main {
    public static void main(String[] args) throws IOException  {
        String code = Files.readString(Paths.get("fizzbuzz.js"));
        Program program = Parser.parse(code);

        Interpreter interpreter = Interpreter.get();
        var output = interpreter.run(program);
        System.out.println(output.toString()); // "buzz".
    }
}

5. Run the application.

mvn exec:java

This should run the application and print "buzz" somewhere in stdout. If you encounter a ClassNotFoundExecption pointing to Main, you probably need this instead:

mvn -X clean install exec:java -Dexec.mainClass="com.my.package.Main" -Dexec.classpathScope=test -e