JavaScript: debugging with embedded Rhino

Mozilla's Rhino engine includes a step-through debugger. It is relatively easy to embed this in your own Java application.

Versions: Rhino 1.7R4 on Java 7.

Running the debugger

// test.js
for(var x = 0; x < 5; x++) {
  java.lang.System.out.println("Hello, World!");
}

Stepping through the above code can be done via this command:

java -cp js.jar org.mozilla.javascript.tools.debugger.Main test.js

This will launch the Swing GUI.

Embedding the debugger

It is relatively easy to do something similar using an embedded engine:

import java.io.*;
import org.mozilla.javascript.*;
import org.mozilla.javascript.tools.debugger.Main;

public class DbgGui {
  public static void main(String[] args) throws IOException {
    String file = "test.js";

    ContextFactory factory = new ContextFactory();

    Main dbg = new Main(file);
    dbg.attachTo(factory);

    Context context = factory.enterContext();
    ScriptableObject scope = context.initStandardObjects();

    // redirect std I/O
    System.setIn(dbg.getIn());
    System.setOut(dbg.getOut());
    System.setErr(dbg.getErr());

    dbg.setBreakOnEnter(true);
    dbg.setScope(scope);
    dbg.setSize(640, 400);
    dbg.setVisible(true);
    dbg.setExitAction(new ExitOnClose());

    try (Reader reader = new FileReader(file)) {
      context.evaluateReader(scope, reader, file, 1, null);
    }
  }

  private static class ExitOnClose implements Runnable {
    @Override
    public void run() {
      System.exit(0);
    }
  }
}