index.js

var fs = require('fs'),
    path = require('path'),
    http = require('http'),
    exec = require('child_process').exec;

var LOG_PREFIX = '[autoupdate]: ';

var pkg = (function find(dir) {

    var pkg = path.join(dir, 'package.json'),
        parent;

    if (fs.existsSync(pkg)) {
        return JSON.parse(fs.readFileSync(pkg, 'utf8')||{});
    }
    parent = path.join(dir, '../');
    if (parent === dir) {
        throw new Error('package.json not found');
    }
    return find(parent);

}(path.dirname(module.parent.filename)));

module.exports = function (callback) {
    var registry = (pkg.publishConfig && pkg.publishConfig.registry) || 'http://registry.npmjs.org',
        pkgUrl = registry + '/' + pkg.name;

    http.get(pkgUrl, function (res) {
        var data = [] ;

        if (res.statusCode !== 200) {
            return error(new Error('response statusCode: '+ res.statusCode));
        }

        res.on('data', function (chunk) {
            data.push(chunk);
        });
        res.on('end', function () {
            var command,latest;

            try{
                lastest = JSON.parse(Buffer.concat(data).toString())['dist-tags']['latest'] ;
            }catch(err){
                return error(err);
            }

            if (latest == pkg.version) {
                console.log(LOG_PREFIX + 'You are currently on the latest version (%s)', pkg.name);
                return callback(null, lastest);
            }
            command = 'npm install ' + pkg.name + '@' + latest + ' --registry=' + registry ;
            console.log(LOG_PREFIX + 'New version found (%s@%s)', pkg.name, latest);

            exec(command, function (err) {
                if (err) {
                    return error(err);
                }
                console.log(LOG_PREFIX + 'Updated to %s (%s)', latest, pkg.name);
                callback(null, lastest);
            });
        });

        res.on('error',function (err){
            error(err);
        });
    });

    function error(err){
        console.error(LOG_PREFIX  + 'Failed to update the new version (%s)', pkg.name);
        console.error(err && err.message);
        callback(err);
    }

};