index.js

var fs = require('fs');
var parse = require('xml-parser');

var args = process.argv.splice(2);
var pomPath = args.length ? args[0] : 'pom.xml';
var packagePath = args.length >= 2 ? args[1] : 'package.json';

main(pomPath, packagePath);

function main (pomPath, packagePath) {
  var pomContent = fs.readFileSync(pomPath, 'utf8');
  var pom = parse(pomContent);
  var pomVersionNode = extractPomVersionNode(pom.root);
  if (!pomVersionNode) {
      var parent = extractParentNode(pom.root);
      pomVersionNode = extractPomVersionNode(parent);
  }

  var pomVersion = pomVersionNode.content.replace(/[\.-](RELEASE|FINAL)$/i, '');

  console.log('found version ' + pomVersion + ' in pom.xml');

  var packageContent = fs.readFileSync(packagePath, 'utf8');
  var packageVersion = JSON.parse(packageContent).version;

  console.log('found version ' + packageVersion + ' in package.json');

  if (pomVersion.endsWith('-SNAPSHOT')) {
      pomVersion = pomVersion.replace('-SNAPSHOT', '');
      console.log('Removed -SNAPSHOT from pom version, as it does not complies with npm versioning system.');
  }

  if (pomVersion === packageVersion) {
    return;
  }

  var newPackageContent = packageContent.replace(formatVersion(packageVersion), formatVersion(pomVersion));
  fs.writeFileSync(packagePath, newPackageContent, 'utf8');

  console.log('package.json updated to version ' + pomVersion);
}

function extractParentNode(node) {
    return node.children.filter(function (item) {
        return item.name === 'parent';
    })[0];
}

function extractPomVersionNode(parent) {
    return parent.children.filter(function (item) {
        return item.name === 'version';
    })[0];
}

function formatVersion (version) { return '"version": "' + version + '"'; }