jsstack - pstack like tool for node.js apps

jsstack.js

#!/usr/bin/env node
"use strict";

var debug = require('_debugger');
var c = new debug.Client();

function main() {
  console.log('requesting trace');
  c.reqBacktrace(function(err,trace) {
    if (!err) {
      trace.frames.forEach(function(frame) {
        process.stderr.write(frame.text + '\n');
      });
      process.exit(0);
    } else {
      console.error(err);
      process.exit(1);
    }
  });
}

function usage() {
  var procname = process.argv[1].split('/').pop()
  console.log('Usage: ' + procname +  ' <pid of node process>');
  process.exit(1);
}

c.on('error', function() {
  console.log('[Failed]');
});

c.once('ready', function() {
  console.log('[ok]');
  c.reqVersion(function(err,version,state) {
    console.log('v8: ' + version); 
    main();
  });
});

if (process.argv.length < 3)
  usage();

var pid = process.argv[2];
process.kill(pid,'SIGUSR1');

setTimeout(function() {
process.stdout.write('connecting ... ');
c.connect(5858);
}, 500);

Hello.
I want to use this code. But I don't know the _debugger module.
Is the module in npm?